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<!DOCTYPE html><html lang="zh-CN"><head><title>软件技术基础</title><meta property="og:title" content="软件技术基础"><meta charset="UTF-8"><meta name="viewport" content="width=device-width,height=device-height,initial-scale=1.0"><meta name="apple-mobile-web-app-capable" content="yes"><meta http-equiv="X-UA-Compatible" content="ie=edge"><meta property="og:type" content="website"><meta name="twitter:card" content="summary"><style>@media screen{body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button,body[data-bespoke-view=next] .bespoke-marp-parent>.bespoke-marp-osc>button,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button{appearance:none;background-color:initial;border:0;color:inherit;cursor:pointer;font-size:inherit;opacity:.8;outline:none;padding:0;transition:opacity .2s 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:is(h1, marp-h1){font-size:2em;margin-block:0.67em}div#\:\$p > svg > foreignObject > section video::-webkit-media-controls{will-change:transform}@page {size:1280px 720px;margin:0}@media print{html, body{background-color:#fff;margin:0;page-break-inside:avoid;break-inside:avoid-page}div#\:\$p > svg > foreignObject > section{page-break-before:always;break-before:page}div#\:\$p > svg > foreignObject > section, div#\:\$p > svg > foreignObject > section *{-webkit-print-color-adjust:exact!important;animation-delay:0s!important;animation-duration:0s!important;color-adjust:exact!important;print-color-adjust:exact!important;transition:none!important}div#\:\$p > svg[data-marpit-svg]{display:block;height:100vh;width:100vw}}div#\:\$p > svg > foreignObject > :where(section){container-type:size}div#\:\$p > svg > foreignObject > section img[data-marp-twemoji]{background:transparent;height:1em;margin:0 .05em 0 .1em;vertical-align:-.1em;width:1em}/*!
* Marp / Marpit Gaia theme.
*
* @theme gaia
* @author Yuki Hattori
*
* @auto-scaling true
* @size 16:9 1280px 720px
* @size 4:3 960px 720px
*/div#\:\$p > svg > foreignObject > section :is(pre, marp-pre) code.hljs{display:block;overflow-x:auto;padding:1em}div#\:\$p > svg > foreignObject > section code.hljs{padding:3px 5px}div#\:\$p > svg > foreignObject > section .hljs{background:#000;color:#f8f8f8}div#\:\$p > svg > foreignObject > section .hljs-comment,div#\:\$p > svg > foreignObject > section .hljs-quote{color:#aeaeae;font-style:italic}div#\:\$p > svg > foreignObject > section .hljs-keyword,div#\:\$p > svg > foreignObject > section .hljs-selector-tag,div#\:\$p > svg > foreignObject > section .hljs-type{color:#e28964}div#\:\$p > svg > foreignObject > section .hljs-string{color:#65b042}div#\:\$p > svg > foreignObject > section .hljs-subst{color:#daefa3}div#\:\$p > svg > foreignObject > section .hljs-link,div#\:\$p > svg > foreignObject > section .hljs-regexp{color:#e9c062}div#\:\$p > svg > foreignObject > section .hljs-name,div#\:\$p > svg > foreignObject > section .hljs-section,div#\:\$p > svg > foreignObject > section 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marp-h3) strong,div#\:\$p > svg > foreignObject > section :is(h4, marp-h4) strong,div#\:\$p > svg > foreignObject > section :is(h5, marp-h5) strong,div#\:\$p > svg > foreignObject > section :is(h6, marp-h6) strong{font-weight:inherit}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h2, marp-h2)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h3, marp-h3)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h4, marp-h4)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h5, marp-h5)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h6, marp-h6)::part(auto-scaling){max-height:580px}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1){font-size:1.8em}div#\:\$p > svg > foreignObject > section :is(h2, marp-h2){font-size:1.5em}div#\:\$p > svg > foreignObject > section :is(h3, marp-h3){font-size:1.3em}div#\:\$p > svg > foreignObject > section :is(h4, 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:is(pre, marp-pre)::part(auto-scaling){max-height:calc(580px - 1em)}div#\:\$p > svg > foreignObject > section blockquote{margin:1em 0 0;padding:0 1em;position:relative}div#\:\$p > svg > foreignObject > section blockquote:after,div#\:\$p > svg > foreignObject > section blockquote:before{content:"“";display:block;font-family:Times New Roman,serif;font-weight:700;position:absolute}div#\:\$p > svg > foreignObject > section blockquote:before{left:0;top:0}div#\:\$p > svg > foreignObject > section blockquote:after{bottom:0;right:0;transform:rotate(180deg)}div#\:\$p > svg > foreignObject > section blockquote>:first-child{margin-top:0}div#\:\$p > svg > foreignObject > section mark{background:transparent}div#\:\$p > svg > foreignObject > section table{border-collapse:collapse;border-spacing:0;margin:1em 0 0}div#\:\$p > svg > foreignObject > section table td,div#\:\$p > svg > foreignObject > section table th{border-style:solid;border-width:1px;padding:.2em .4em}div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header,div#\:\$p > svg > foreignObject > section:after{box-sizing:border-box;font-size:66%;height:70px;line-height:50px;overflow:hidden;padding:10px 25px;position:absolute}div#\:\$p > svg > foreignObject > section:after{--marpit-root-font-size:66%;}div#\:\$p > svg > foreignObject > section header{top:0}div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header{left:0;right:0}div#\:\$p > svg > foreignObject > section footer{bottom:0}div#\:\$p > svg > foreignObject > section{background-color:var(--color-background);background-image:linear-gradient(135deg, hsla(0,0%,53%,0), hsla(0,0%,53%,.02) 50%, hsla(0,0%,100%,0) 0, hsla(0,0%,100%,.05));color:var(--color-foreground);font-family:Lato,Avenir Next,Avenir,Trebuchet MS,Segoe UI,sans-serif;font-size:35px;height:720px;letter-spacing:1.25px;line-height:1.35;padding:70px;width:1280px;word-wrap:break-word;--color-background:#fff8e1;--color-background-stripe:rgba(69,90,100,.1);--color-foreground:#455a64;--color-dimmed:#6a7a7d;--color-highlight:#0288d1;}div#\:\$p > svg > foreignObject > section{--marpit-root-font-size:35px;}div#\:\$p > svg > foreignObject > section:after{bottom:0;font-size:80%;right:0}div#\:\$p > svg > foreignObject > section:after{--marpit-root-font-size:80%;}div#\:\$p > svg > foreignObject > section a,div#\:\$p > svg > foreignObject > section mark{color:var(--color-highlight)}div#\:\$p > svg > foreignObject > section code{background:var(--color-dimmed);color:var(--color-background)}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1) strong,div#\:\$p > svg > foreignObject > section :is(h2, marp-h2) strong,div#\:\$p > svg > foreignObject > section :is(h3, marp-h3) strong,div#\:\$p > svg > foreignObject > section :is(h4, marp-h4) strong,div#\:\$p > svg > foreignObject > section :is(h5, marp-h5) strong,div#\:\$p > svg > foreignObject > section :is(h6, marp-h6) strong{color:var(--color-highlight)}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre){background:var(--color-foreground)}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre)>code{background:transparent}div#\:\$p > svg > foreignObject > section blockquote:after,div#\:\$p > svg > foreignObject > section blockquote:before,div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header,div#\:\$p > svg > foreignObject > section section:after{color:var(--color-dimmed)}div#\:\$p > svg > foreignObject > section table td,div#\:\$p > svg > foreignObject > section table th{border-color:var(--color-foreground)}div#\:\$p > svg > foreignObject > section table thead th{background:var(--color-foreground);color:var(--color-background)}div#\:\$p > svg > foreignObject > section table tbody>tr:nth-child(odd) td,div#\:\$p > svg > foreignObject > section table tbody>tr:nth-child(odd) th{background:var(--color-background-stripe, transparent)}div#\:\$p > svg > foreignObject > section>:first-child,div#\:\$p > svg > foreignObject > section>header:first-child+*{margin-top:0}div#\:\$p > svg > foreignObject > section:where(.invert){--color-background:#455a64;--color-background-stripe:rgba(255,248,225,.1);--color-foreground:#fff8e1;--color-dimmed:#dad8c8;--color-highlight:#81d4fa;}div#\:\$p > svg > foreignObject > section:where(.gaia){--color-background:#0288d1;--color-background-stripe:rgba(255,248,225,.1);--color-foreground:#fff8e1;--color-dimmed:#cce2de;--color-highlight:#81d4fa;}div#\:\$p > svg > foreignObject > section:where(.lead){align-items:stretch;flex-flow:column nowrap;place-content:safe center center}div#\:\$p > svg > foreignObject > section:where(.lead) :is(h1, marp-h1),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h2, marp-h2),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h3, marp-h3),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h4, marp-h4),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h5, marp-h5),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h6, marp-h6){text-align:center}div#\:\$p > svg > foreignObject > section:where(.lead) p{text-align:center}div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h1, marp-h1),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h2, marp-h2),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h3, marp-h3),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h4, marp-h4),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h5, marp-h5),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h6, marp-h6),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>p{text-align:left}div#\:\$p > svg > foreignObject > section:where(.lead) ol>li>p,div#\:\$p > svg > foreignObject > section:where(.lead) ul>li>p{text-align:left}div#\:\$p > svg > foreignObject > section:where(.lead) table{margin-left:auto;margin-right:auto}div#\:\$p > svg > foreignObject > section[data-marpit-scope-toh4rbuQ] .columns{display:grid;grid-template-columns:3fr 4fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-NtuWZ2TB] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-NtuWZ2TB] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-NtuWZ2TB] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-LtUjfZmK] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-hFPytUhP] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-LypbSXgm] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-uWsSWJ9M] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-Xi8sD0g4] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-OvsytdcM] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-20AmLKUo] li{font-size:27px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-jP4JqBAC] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-UCLMo4k4] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-SbMSQmQP] strong{color:red}div#\:\$p > svg > foreignObject > section[data-marpit-scope-wVyQiMui] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-wVyQiMui] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-wVyQiMui] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-6lldkuav] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-fA8k4zgI] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-fA8k4zgI] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-fA8k4zgI] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-KNw2tNPf] .columns{display:grid;grid-template-columns:2fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-TwWPiBRh] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-gjMqOQe9] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-q29C4H0F] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-tO56kWge] .columns{display:grid;grid-template-columns:2fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-oYIY3MYP] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-oYIY3MYP] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-oYIY3MYP] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-FslrECZu] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-j66SLmHq] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-j66SLmHq] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-j66SLmHq] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-50mKTgY1] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-CdwqGNAX] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-mjh6ti3v] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-mjh6ti3v] strong{color:red}div#\:\$p > svg > foreignObject > section[data-marpit-scope-2VWQcanH] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-2VWQcanH] strong{color:red}div#\:\$p > svg > foreignObject > section[data-marpit-scope-XGyfVN5G] .columns{display:grid;grid-template-columns:3fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-S1ewwLpj] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-S1ewwLpj] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-S1ewwLpj] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-49W13sHR] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-4js3uptA] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-4y31Y5nA] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-4y31Y5nA] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-4y31Y5nA] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-92HZDn5f] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-RGjmv69S] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-p1K4gJdv] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-p1K4gJdv] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-p1K4gJdv] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-rvZhcdaN] strong{color:red}div#\:\$p > svg > foreignObject > section[data-marpit-scope-hFCeJd4J] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-hFCeJd4J] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-hFCeJd4J] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-RJaeLPTG] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-RJaeLPTG] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-s18QLH24] table{font-size:30px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-s18QLH24] .columns{display:grid;grid-template-columns:1fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-Q72Uly6U] table{font-size:30px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-Q72Uly6U] .columns{display:grid;grid-template-columns:2fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-scope-lpc3HDLl] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-lpc3HDLl] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-lpc3HDLl] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-XVgeSLKU] :is(h2, marp-h2){font-size:10px;opacity:0}div#\:\$p > svg > foreignObject > section[data-marpit-scope-XVgeSLKU] strong{font-size:60px}div#\:\$p > svg > foreignObject > section[data-marpit-scope-XVgeSLKU] p{text-align:center}div#\:\$p > svg > foreignObject > section[data-marpit-scope-cRnFwrXj] .columns{display:grid;grid-template-columns:2fr 1fr;gap:calc(var(--marpit-root-font-size, 1rem) * 2)}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]{columns:initial!important;display:block!important;padding:0!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]::before, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]::after, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"]::before, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"]::after{display:none!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container]{all:initial;display:flex;flex-direction:row;height:100%;overflow:hidden;width:100%}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container][data-marpit-advanced-background-direction="vertical"]{flex-direction:column}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"][data-marpit-advanced-background-split] > div[data-marpit-advanced-background-container]{width:var(--marpit-advanced-background-split, 50%)}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"][data-marpit-advanced-background-split="right"] > div[data-marpit-advanced-background-container]{margin-left:calc(100% - var(--marpit-advanced-background-split, 50%))}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container] > figure{all:initial;background-position:center;background-repeat:no-repeat;background-size:cover;flex:auto;margin:0}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container] > figure > figcaption{position:absolute;border:0;clip:rect(0, 0, 0, 0);height:1px;margin:-1px;overflow:hidden;padding:0;white-space:nowrap;width:1px}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"], div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="pseudo"]{background:transparent!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="pseudo"], div#\:\$p > svg[data-marpit-svg] > foreignObject[data-marpit-advanced-background="pseudo"]{pointer-events:none!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background-split]{width:100%;height:100%}
</style></head><body><div class="bespoke-marp-osc"><button data-bespoke-marp-osc="prev" tabindex="-1" title="Previous slide">Previous slide</button><span data-bespoke-marp-osc="page"></span><button data-bespoke-marp-osc="next" tabindex="-1" title="Next slide">Next slide</button><button data-bespoke-marp-osc="fullscreen" tabindex="-1" title="Toggle fullscreen (f)">Toggle fullscreen</button><button data-bespoke-marp-osc="presenter" tabindex="-1" title="Open presenter view (p)">Open presenter view</button></div><div id=":$p"><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="1" data-paginate="true" data-class="lead" data-theme="gaia" lang="zh-CN" class="lead" data-marpit-pagination="1" style="--paginate:true;--class:lead;--theme:gaia;" data-marpit-pagination-total="108">
<h1 id="%E8%BD%AF%E4%BB%B6%E6%8A%80%E6%9C%AF%E5%9F%BA%E7%A1%80">软件技术基础</h1>
<h2 id="%E6%8C%87%E9%92%88">指针</h2>
<p><strong>施展</strong><br />
武汉光电国家研究中心 & 计算机学院<br />
华中科技大学</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="2" data-marpit-scope-toh4rbuQ="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="2" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E4%B8%BB%E8%A6%81%E5%86%85%E5%AE%B9">主要内容</h2>
<div class="columns">
<div>
<ul>
<li>指针的<strong>基本概念与操作</strong></li>
<li>指针作为<strong>函数参数</strong>的使用</li>
<li>指针与<strong>一维数组的关系</strong></li>
<li>指针与<strong>字符串的处理</strong></li>
<li>指针数组与<strong>二级指针</strong></li>
</ul>
</div>
<div>
<ul>
<li>带参数的main函数与<strong>命令行参数</strong></li>
<li><strong>指针函数</strong>与<strong>函数指针</strong></li>
<li>指针与<strong>二维数组的关系</strong></li>
<li>复杂指针声明与<strong>typedef</strong>使用</li>
</ul>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="3" data-marpit-scope-NtuWZ2TB="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="3" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%9A%84%E6%A6%82%E5%BF%B5">指针的概念</h2>
<p><a href="#%E6%8C%87%E9%92%88%E7%9A%84%E6%A6%82%E5%BF%B5"><strong>指针的概念</strong></a><br />
<a href="#%E6%8C%87%E9%92%88%E5%8F%82%E6%95%B0">指针参数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E4%B8%80%E7%BB%B4%E6%95%B0%E7%BB%84">指针和一维数组</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E5%AD%97%E7%AC%A6%E4%B8%B2">指针和字符串</a><br />
<a href="#%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84">指针数组</a><br />
<a href="#%E5%B8%A6%E5%8F%82%E6%95%B0%E7%9A%84main%E5%87%BD%E6%95%B0">带参数的main函数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%87%BD%E6%95%B0">指针函数</a><br />
<a href="#%E5%87%BD%E6%95%B0%E7%9A%84%E6%8C%87%E9%92%88">函数的指针</a><br />
<a href="#%E6%8C%87%E9%92%88%E4%B8%8E%E4%BA%8C%E7%BB%B4%E6%95%B0%E7%BB%84">指针与二维数组</a><br />
<a href="#%E7%94%A8typedef%E5%AE%9A%E4%B9%89%E7%B1%BB%E5%9E%8B">用typedef定义类型</a><br />
<a href="#%E5%A4%8D%E6%9D%82%E5%A3%B0%E6%98%8E">复杂声明</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="4" data-marpit-scope-LtUjfZmK="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="4" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%8F%98%E9%87%8F%E4%B8%8E%E5%9C%B0%E5%9D%80">变量与地址</h2>
<div class="columns">
<div>
<ul>
<li>变量占有一定量（根据类型）的连续存储单元</li>
</ul>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">short</span> x;
<span class="hljs-type">char</span> a[<span class="hljs-number">5</span>];
</code></pre>
<ul>
<li>变量的连续存储单元首地址称为<strong>变量的地址</strong></li>
</ul>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c">&x, a <= => &a[<span class="hljs-number">0</span>]
</code></pre>
<ul>
<li><strong>思考</strong>: 地址数据又是什么类型的变量?</li>
</ul>
</div>
<div>
<p><img src="images/c-pointer-concept.png" alt="" style="width:300px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="5" data-marpit-scope-hFPytUhP="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="5" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E5%AE%9A%E4%B9%89">指针定义</h2>
<div class="columns">
<div>
<ul>
<li>
<p><strong>指针</strong>: 变量的地址</p>
<ul>
<li><code>&x</code>: 指针常量</li>
<li><code>p</code>: 指针变量</li>
</ul>
</li>
<li>
<p><strong>指针变量</strong>: 存放地址数据的变量</p>
<ul>
<li>指针变量也是一种变量，也要<strong>占用一定的内存单元</strong></li>
<li>特殊之处在于它存放的是另一个变量所占存储单元的<strong>起始地址</strong></li>
</ul>
</li>
</ul>
</div>
<div>
<p><img src="images/c-pointer-concept-1.png" alt="" style="width:300px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="6" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="6" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E5%8F%98%E9%87%8F%E7%9A%84%E5%A3%B0%E6%98%8E">指针变量的声明</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c">数据类型 *标识符;
</code></pre>
<p>↑所指变量的数据类型</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">short</span> x = <span class="hljs-number">1</span>, y = <span class="hljs-number">2</span>, a[<span class="hljs-number">10</span>], *p;
p = &x; <span class="hljs-comment">// √</span>
p = a; <span class="hljs-comment">// √</span>
p = a[<span class="hljs-number">0</span>]; <span class="hljs-comment">// ×</span>
</code></pre>
<p><strong>思考</strong>: 为什么使用指针？</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="7" data-marpit-scope-LypbSXgm="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="7" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E4%B8%BA%E4%BB%80%E4%B9%88%E4%BD%BF%E7%94%A8%E6%8C%87%E9%92%88">为什么使用指针？</h2>
<div class="columns">
<div>
<p><strong>直接访问</strong>: 通过变量名存取变量</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c">x = <span class="hljs-number">0x1234</span>;
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%x"</span>, x);
</code></pre>
<p><strong>间接访问</strong>: 通过变量的地址存取变量</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c">p = &x;
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%x"</span>, *p);
</code></pre>
<p>先访问<code>p</code>，得到<code>x</code>的地址，再通过该地址找到它所指向的单元中的值。</p>
</div>
<div>
<p><img src="images/c-pointer-concept-2.png" alt="" style="width:300px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="8" data-marpit-scope-uWsSWJ9M="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="8" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E8%BF%90%E7%AE%97%E7%AC%A6">指针运算符 <code>*</code></h2>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">short</span> x = <span class="hljs-number">1</span>, y = <span class="hljs-number">2</span>, *p; <span class="hljs-comment">// p是short型指针变量</span>
p = &x; <span class="hljs-comment">// 指针p指向x</span>
y = *p; <span class="hljs-comment">// *p<==>x</span>
*p += <span class="hljs-number">10</span>; <span class="hljs-comment">// x+=10</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"x=%hd,y=%hd"</span>, x, y);
</code></pre>
</div>
<div>
<p><img src="images/c-pointer-concept-3.png" alt="" style="width:270px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="9" data-marpit-scope-Xi8sD0g4="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="9" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E8%BF%90%E7%AE%97%E7%AC%A6-1">指针运算符 <code>*</code> …</h2>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">short</span> x = <span class="hljs-number">1</span>, y = <span class="hljs-number">2</span>, *p; <span class="hljs-comment">// p是short型指针变量</span>
p = &x; <span class="hljs-comment">// 指针p指向x</span>
y = *p; <span class="hljs-comment">// *p<==>x</span>
*p += <span class="hljs-number">10</span>; <span class="hljs-comment">// x+=10</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"x=%hd,y=%hd"</span>, x, y);
</code></pre>
<p>输出:</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-bash">x=11, y=1
</code></pre>
<p><strong>思考</strong>: 为什么指针有类型?</p>
</div>
<div>
<p><img src="images/c-pointer-concept-3-1.png" alt="" style="width:270px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="10" data-marpit-scope-OvsytdcM="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="10" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E4%B8%BA%E4%BB%80%E4%B9%88%E6%8C%87%E9%92%88%E6%9C%89%E7%B1%BB%E5%9E%8B">为什么指针有类型？</h2>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> x = <span class="hljs-number">0x1234ABCD</span>, a, b, *p1;
<span class="hljs-type">char</span> *p2;
p1 = &x; p2 = (<span class="hljs-type">char</span> *)&x;
a = *p1; b = *p2;
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%x,%x"</span>, a, b); <span class="hljs-comment">// 输出: 1234ABCD,CD</span>
b = *(p2 + <span class="hljs-number">1</span>);
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%x"</span>, b); <span class="hljs-comment">// 后面谈移动也与之有关</span>
</code></pre>
</div>
<div>
<p><img src="images/c-pointer-type.png" alt="" style="width:270px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="11" data-marpit-scope-20AmLKUo="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="11" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%BB%83%E4%B9%A0%E4%B8%80">指针练习一</h2>
<ol>
<li>
<p><strong>检测机器的大小端模式</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> <span class="hljs-title function_">checkEndion</span><span class="hljs-params">(<span class="hljs-type">void</span>)</span>; <span class="hljs-comment">// 返回1小端，0大端</span>
</code></pre>
</li>
<li>
<p><strong>定义宏提取16位数据的高八位和低八位</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">define</span> BYTE0(hdata) ________</span>
<span class="hljs-meta">#<span class="hljs-keyword">define</span> BYTE1(hdata) ________</span>
</code></pre>
</li>
<li>
<p><strong>将int数的最高字节和最低字节交换</strong></p>
</li>
<li>
<p><strong>将32位整数IP转为点分十进制输出</strong></p>
</li>
<li>
<p><strong>32位本机字节序与网络字节序之间的转换</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">unsigned</span> <span class="hljs-type">long</span> <span class="hljs-title function_">hton</span><span class="hljs-params">(<span class="hljs-type">unsigned</span> <span class="hljs-type">long</span> h)</span>; <span class="hljs-comment">// hton(0x1234)值为0x34120000</span>
</code></pre>
</li>
</ol>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="12" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="12" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%82%AC%E6%8C%82%E6%8C%87%E9%92%88">悬挂指针</h2>
<p>下面程序段存在什么问题？</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> x, *p; <span class="hljs-comment">// p是一个整型指针变量，其值不确定</span>
x = <span class="hljs-number">25</span>;
*p = x; <span class="hljs-comment">// 使用悬挂指针，错！</span>
<span class="hljs-built_in">scanf</span>(<span class="hljs-string">"%d"</span>, p); <span class="hljs-comment">// 使用悬挂指针，错！</span>
</code></pre>
<p><strong>悬挂指针（野指针）</strong>: 指针的声明只是创建了指针变量，但并没有指向具体的变量，此时指针的值是不确定的随机值。</p>
<p>野指针<strong>可能导致程序访问非法内存地址</strong>，造成程序崩溃或数据损坏等严重后果。</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="13" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="13" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%9A%84%E7%A7%BB%E5%8A%A8%E6%93%8D%E4%BD%9C">指针的移动操作</h2>
<p>运算符：<code>+, -, ++, --, +=, -=</code></p>
<p><strong>指针的移动</strong>：指针在原有位置的基础上，通过加一个整数实现指针的<strong>前移</strong>（地址增大的方向）或者通过减一个整数实现指针的<strong>后移</strong>。</p>
<p><code>p ± k</code> - 指针p前移/后移k个元素</p>
<p>↑<em>指针</em> ↑<em>整数</em></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="14" data-marpit-scope-jP4JqBAC="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="14" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%A7%BB%E5%8A%A8%E7%A4%BA%E4%BE%8B">指针移动示例</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> x[<span class="hljs-number">5</span>] = {<span class="hljs-number">1</span>, <span class="hljs-number">3</span>, <span class="hljs-number">5</span>, <span class="hljs-number">7</span>, <span class="hljs-number">9</span>}, *px = &x[<span class="hljs-number">1</span>];
</code></pre>
<div class="columns">
<div>
<table>
<thead>
<tr>
<th>表达式</th>
<th>值</th>
</tr>
</thead>
<tbody>
<tr>
<td><code>++*px</code></td>
<td>4</td>
</tr>
<tr>
<td><code>*++px</code></td>
<td>5</td>
</tr>
<tr>
<td><code>*(--px)</code></td>
<td>1</td>
</tr>
<tr>
<td><code>*(px--)</code></td>
<td>3</td>
</tr>
<tr>
<td><code>*px++</code></td>
<td>3</td>
</tr>
<tr>
<td><code>px += 2, *px</code></td>
<td>7</td>
</tr>
</tbody>
</table>
</div>
<div>
<p><img src="images/c-pointer-op.png" alt="" style="width:300px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="15" data-marpit-scope-UCLMo4k4="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="15" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%9A%84%E7%A7%BB%E5%8A%A8%E5%92%8C%E7%B1%BB%E5%9E%8B%E6%9C%89%E5%85%B3">指针的移动和类型有关</h2>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> x = <span class="hljs-number">0x1234ABCD</span>, a, b, *p1;
<span class="hljs-type">char</span> *p2;
p1 = &x; p2 = (<span class="hljs-type">char</span> *)&x;
a = *p1; b = *p2;
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%x,%x"</span>, a, b); <span class="hljs-comment">// 1234ABCD,CD</span>
b = *(p2 + <span class="hljs-number">1</span>);
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%x"</span>, b); <span class="hljs-comment">// AB</span>
</code></pre>
</div>
<div>
<p><img src="images/c-pointer-type.png" alt="" style="width:300px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="16" data-marpit-scope-SbMSQmQP="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="16" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%9A%84%E8%B5%8B%E5%80%BC%E8%BF%90%E7%AE%97">指针的赋值运算</h2>
<p><strong>同类型</strong>的指针可以直接赋值</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a[<span class="hljs-number">3</span>] = {<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>}, x, *p, *q;
p = a; q = &x;
</code></pre>
<p><strong>不同类型</strong>的指针必须使用<strong>类型强制转换</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">long</span> x;
<span class="hljs-type">char</span> *p;
p = (<span class="hljs-type">char</span> *)&x;
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="17" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="17" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%9A%84%E5%BA%94%E7%94%A8">指针的应用</h2>
<p>例：一个长整型数占4个字节，从低字节开始依次取出每个字节的高4位和低4位并以十六进制字符形式显示。</p>
<p><img src="images/c-pointer-example.png" alt="" style="height:350px;" /></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="18" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="18" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h3 id="%E5%AE%8C%E6%95%B4%E4%BE%8B%E7%A8%8B">完整例程</h3>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">include</span> <span class="hljs-string"><stdio.h></span></span>
<span class="hljs-type">int</span> <span class="hljs-title function_">main</span><span class="hljs-params">(<span class="hljs-type">void</span>)</span> {
<span class="hljs-type">long</span> x = <span class="hljs-number">0x1234ABCD</span>, k;
<span class="hljs-type">char</span> *p = (<span class="hljs-type">char</span> *)&x; <span class="hljs-comment">// 强制转换成char型指针</span>
<span class="hljs-type">char</span> up_half, low_half;
<span class="hljs-keyword">for</span>(k = <span class="hljs-number">0</span>; k < <span class="hljs-number">4</span>; k++) { <span class="hljs-comment">// 循环4次，顺序访问每个字节</span>
low_half = (*p) & <span class="hljs-number">0x0f</span>; <span class="hljs-comment">// 取低4位</span>
<span class="hljs-keyword">if</span>(low_half < <span class="hljs-number">10</span>) low_half += <span class="hljs-string">'0'</span>; <span class="hljs-comment">// 转换成字符0-9</span>
<span class="hljs-keyword">else</span> low_half = (low_half - <span class="hljs-number">10</span>) + <span class="hljs-string">'A'</span>; <span class="hljs-comment">// 转换成字符A-F</span>
up_half = (*p >> <span class="hljs-number">4</span>) & <span class="hljs-number">0x0f</span>; <span class="hljs-comment">// 取高4位</span>
<span class="hljs-keyword">if</span>(up_half < <span class="hljs-number">10</span>) up_half |= <span class="hljs-string">'0'</span>;
<span class="hljs-keyword">else</span> up_half = (up_half - <span class="hljs-number">10</span>) + <span class="hljs-string">'A'</span>;
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%c %c\n"</span>, up_half, low_half);
p++; <span class="hljs-comment">// 指向长整数4个字节中的下一个字节</span>
}
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="19" data-marpit-scope-wVyQiMui="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="19" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E5%8F%82%E6%95%B0">指针参数</h2>
<p><a href="#%E6%8C%87%E9%92%88%E7%9A%84%E6%A6%82%E5%BF%B5">指针的概念</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%8F%82%E6%95%B0"><strong>指针参数</strong></a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E4%B8%80%E7%BB%B4%E6%95%B0%E7%BB%84">指针和一维数组</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E5%AD%97%E7%AC%A6%E4%B8%B2">指针和字符串</a><br />
<a href="#%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84">指针数组</a><br />
<a href="#%E5%B8%A6%E5%8F%82%E6%95%B0%E7%9A%84main%E5%87%BD%E6%95%B0">带参数的main函数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%87%BD%E6%95%B0">指针函数</a><br />
<a href="#%E5%87%BD%E6%95%B0%E7%9A%84%E6%8C%87%E9%92%88">函数的指针</a><br />
<a href="#%E6%8C%87%E9%92%88%E4%B8%8E%E4%BA%8C%E7%BB%B4%E6%95%B0%E7%BB%84">指针与二维数组</a><br />
<a href="#%E7%94%A8typedef%E5%AE%9A%E4%B9%89%E7%B1%BB%E5%9E%8B">用typedef定义类型</a><br />
<a href="#%E5%A4%8D%E6%9D%82%E5%A3%B0%E6%98%8E">复杂声明</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="20" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="20" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E4%BC%A0%E5%80%BC%E8%B0%83%E7%94%A8">传值调用</h2>
<p>形参的修改无法影响实参变量的值。</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">include</span> <span class="hljs-string"><stdio.h></span></span>
<span class="hljs-type">void</span> <span class="hljs-title function_">swap</span><span class="hljs-params">(<span class="hljs-type">int</span> x, <span class="hljs-type">int</span> y)</span> {
<span class="hljs-type">int</span> t;
t = x; x = y; y = t;
}
<span class="hljs-type">int</span> <span class="hljs-title function_">main</span><span class="hljs-params">(<span class="hljs-type">void</span>)</span> {
<span class="hljs-type">int</span> a = <span class="hljs-number">3</span>, b = <span class="hljs-number">5</span>;
swap(a, b);
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"a=%d,b=%d\n"</span>, a, b); <span class="hljs-comment">// a=3, b=5 保持原样</span>
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="21" data-marpit-scope-6lldkuav="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="21" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E4%BC%A0%E5%9D%80%E8%B0%83%E7%94%A8">传址调用</h2>
<p>以指针作为函数的参数实现变量值的交换。</p>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">include</span> <span class="hljs-string"><stdio.h></span></span>
<span class="hljs-type">void</span> <span class="hljs-title function_">swap</span><span class="hljs-params">(<span class="hljs-type">int</span> *px, <span class="hljs-type">int</span> *py)</span> {
<span class="hljs-type">int</span> t;
t = *px; *px = *py; *py = t;
}
<span class="hljs-type">int</span> <span class="hljs-title function_">main</span><span class="hljs-params">(<span class="hljs-type">void</span>)</span> {
<span class="hljs-type">int</span> a = <span class="hljs-number">10</span>, b = <span class="hljs-number">20</span>, c = <span class="hljs-number">30</span>;
swap(&a, &b);
swap(&b, &c);
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"a=%d,b=%d,c=%d\n"</span>, a, b, c);
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
</code></pre>
</div>
<div>
<p><img src="images/c-pointer-swap.svg" alt="" style="width:300px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="22" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="22" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E4%BD%9C%E5%87%BD%E6%95%B0%E5%8F%82%E6%95%B0">指针作函数参数</h2>
<ul>
<li>改变主调函数中变量的值</li>
<li>使函数送回多个值</li>
</ul>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-comment">// implicit returned values:</span>
<span class="hljs-type">void</span> <span class="hljs-title function_">sum</span><span class="hljs-params">(<span class="hljs-type">int</span> x, <span class="hljs-type">int</span> y, <span class="hljs-type">int</span> *p)</span> {
<span class="hljs-comment">// x, y 入口，*p 出口</span>
*p = x + y;
}
<span class="hljs-comment">// the caller</span>
<span class="hljs-type">int</span> sum;
sum(<span class="hljs-number">3</span>, <span class="hljs-number">4</span>, &sum);
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="23" data-marpit-scope-fA8k4zgI="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="23" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E5%92%8C%E4%B8%80%E7%BB%B4%E6%95%B0%E7%BB%84">指针和一维数组</h2>
<p><a href="#%E6%8C%87%E9%92%88%E7%9A%84%E6%A6%82%E5%BF%B5">指针的概念</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%8F%82%E6%95%B0">指针参数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E4%B8%80%E7%BB%B4%E6%95%B0%E7%BB%84"><strong>指针和一维数组</strong></a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E5%AD%97%E7%AC%A6%E4%B8%B2">指针和字符串</a><br />
<a href="#%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84">指针数组</a><br />
<a href="#%E5%B8%A6%E5%8F%82%E6%95%B0%E7%9A%84main%E5%87%BD%E6%95%B0">带参数的main函数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%87%BD%E6%95%B0">指针函数</a><br />
<a href="#%E5%87%BD%E6%95%B0%E7%9A%84%E6%8C%87%E9%92%88">函数的指针</a><br />
<a href="#%E6%8C%87%E9%92%88%E4%B8%8E%E4%BA%8C%E7%BB%B4%E6%95%B0%E7%BB%84">指针与二维数组</a><br />
<a href="#%E7%94%A8typedef%E5%AE%9A%E4%B9%89%E7%B1%BB%E5%9E%8B">用typedef定义类型</a><br />
<a href="#%E5%A4%8D%E6%9D%82%E5%A3%B0%E6%98%8E">复杂声明</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="24" data-marpit-scope-KNw2tNPf="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="24" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%95%B0%E7%BB%84%E5%85%83%E7%B4%A0%E7%9A%84%E8%A1%A8%E7%A4%BA">数组元素的表示</h2>
<p>数组元素既可以用下标表示，也可以用指针表示。</p>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a[<span class="hljs-number">10</span>], *p = a;
</code></pre>
<table>
<thead>
<tr>
<th>表示方法</th>
<th>元素值</th>
<th>地址</th>
</tr>
</thead>
<tbody>
<tr>
<td>下标法</td>
<td><code>a[i]</code></td>
<td><code>&a[i]</code></td>
</tr>
<tr>
<td>指针法（数组名）</td>
<td><code>*(a+i)</code></td>
<td><code>a+i</code></td>
</tr>
<tr>
<td>指针法（指针变量）</td>
<td><code>*(p+i)</code></td>
<td><code>p+i</code></td>
</tr>
</tbody>
</table>
</div>
<div>
<p><img src="images/c-pointer-to-array.png" alt="" style="width:350px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="25" data-marpit-scope-TwWPiBRh="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="25" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%95%B0%E7%BB%84%E5%85%83%E7%B4%A0%E7%9A%84%E8%BE%93%E5%85%A5">数组元素的输入</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">define</span> N 10</span>
<span class="hljs-type">int</span> a[N], *p, i;
p = a;
</code></pre>
<div class="columns">
<div>
<p><strong>方法1:</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < N; i++)
<span class="hljs-built_in">scanf</span>(<span class="hljs-string">"%d"</span>, &a[i]); <span class="hljs-comment">// 或 a+i, p+i</span>
</code></pre>
<p><strong>方法2:</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-keyword">for</span>(; p < a + N; p++)
<span class="hljs-built_in">scanf</span>(<span class="hljs-string">"%d"</span>, p); <span class="hljs-comment">// 或 p++</span>
</code></pre>
</div>
<div>
<p><strong>候选项</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c">&a[i]
a+i
p+i
p++
a++ <span class="hljs-comment">// 注意！</span>
</code></pre>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="26" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="26" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%95%B0%E7%BB%84%E5%85%83%E7%B4%A0%E7%9A%84%E8%BE%93%E5%87%BA">数组元素的输出</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a[<span class="hljs-number">10</span>], *p, i;
p = a;
</code></pre>
<p><strong>方法1:</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < <span class="hljs-number">10</span>; i++)
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%d"</span>, a[i]); <span class="hljs-comment">// 或 *(a+i), *(p+i), *p++</span>
</code></pre>
<p><strong>方法2:</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-keyword">for</span>(; p < a + <span class="hljs-number">10</span>; p++)
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%d"</span>, *p);
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="27" data-marpit-scope-gjMqOQe9="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="27" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%95%B0%E7%BB%84%E5%85%83%E7%B4%A0%E7%9A%84%E8%BE%93%E5%85%A5%E5%92%8C%E8%BE%93%E5%87%BA">数组元素的输入和输出</h2>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a[<span class="hljs-number">10</span>], *p, i;
<span class="hljs-keyword">for</span>(p = a, i = <span class="hljs-number">0</span>; i < <span class="hljs-number">10</span>; i++)
<span class="hljs-built_in">scanf</span>(<span class="hljs-string">"%d"</span>, p++);
<span class="hljs-keyword">while</span>(p < a + <span class="hljs-number">10</span>) <span class="hljs-comment">// 错误！p已指向数组末尾</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%d"</span>, *p++);
</code></pre>
</div>
<div>
<p><img src="images/c-pointer-to-array-1.png" alt="" style="width:350px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="28" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="28" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E7%9A%84%E5%85%B3%E7%B3%BB%E8%BF%90%E7%AE%97">指针的关系运算</h2>
<p><code><</code>, <code><=</code>, <code>></code>, <code>>=</code>, <code>==</code>, <code>!=</code></p>
<ul>
<li>只限于同类型指针</li>
<li>不同类型指针之间的关系运算被视为非法操作</li>
</ul>
<p><strong>前例正确做法：</strong></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a[<span class="hljs-number">10</span>], *p = a;
<span class="hljs-keyword">while</span>(p < a + <span class="hljs-number">10</span>) <span class="hljs-comment">// 正序输出数组a的全部元素</span>
<span class="hljs-built_in">scanf</span>(<span class="hljs-string">"%d"</span>, p++);
<span class="hljs-keyword">while</span>(p > a) <span class="hljs-comment">// 逆序输出数组a的全部元素</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%d"</span>, *--p);
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="29" data-marpit-scope-q29C4H0F="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="29" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h3 id="%E4%B8%A4%E4%B8%AA%E6%8C%87%E9%92%88%E7%9B%B8%E5%87%8F">两个指针相减</h3>
<div class="columns">
<div>
<p>两个指针指向同一数组的元素，可以相减</p>
<p><code>pa2 – pa1</code> 等于所指元素的下标相减</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> <span class="hljs-title function_">strlen</span><span class="hljs-params">(<span class="hljs-type">char</span> s[])</span> { <span class="hljs-comment">// 等价于 int strlen(char *s)</span>
<span class="hljs-type">char</span> *q = s;
<span class="hljs-keyword">while</span>(*s) s++;
<span class="hljs-keyword">return</span> (s - q);
}
</code></pre>
</div> <div>
<p><img src="images/c-pointer-sub.png" alt="" style="width:220px;" /></p>
</div> </div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="30" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="30" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%B8%B8%E9%87%8F%E6%8C%87%E9%92%88">常量指针</h2>
<p>指向常量的指针</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a = <span class="hljs-number">5</span>, b = <span class="hljs-number">6</span>;
<span class="hljs-type">const</span> <span class="hljs-type">int</span> *p; <span class="hljs-comment">// p是常量指针，可以不初始化</span>
p = &a; <span class="hljs-comment">// 合法，可以修改指针本身的值</span>
*p = <span class="hljs-number">10</span>; <span class="hljs-comment">// 非法，不能通过p修改所指变量a的值</span>
a = <span class="hljs-number">8</span>; <span class="hljs-comment">// 合法，因为a不是常量</span>
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="31" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="31" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E5%B8%B8%E9%87%8F">指针常量</h2>
<p>类型是指针的常量</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a = <span class="hljs-number">5</span>, b = <span class="hljs-number">6</span>;
<span class="hljs-type">int</span> *<span class="hljs-type">const</span> p = &a; <span class="hljs-comment">// p是指针常量，必须初始化</span>
*p = <span class="hljs-number">10</span>; <span class="hljs-comment">// 合法，可以使用p修改所指对象的值</span>
p = &b; <span class="hljs-comment">// 非法，它不能再指向别的变量</span>
<span class="hljs-type">int</span> x[<span class="hljs-number">10</span>]; <span class="hljs-comment">// x是指针常量</span>
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="32" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="32" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E5%90%91%E5%B8%B8%E9%87%8F%E7%9A%84%E6%8C%87%E9%92%88%E5%B8%B8%E9%87%8F">指向常量的指针常量</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> a = <span class="hljs-number">5</span>, b = <span class="hljs-number">6</span>;
<span class="hljs-type">const</span> <span class="hljs-type">int</span> *<span class="hljs-type">const</span> p = &a; <span class="hljs-comment">// p是指向常量的指针常量，必须初始化</span>
*p = <span class="hljs-number">10</span>; <span class="hljs-comment">// 非法，不能通过p修改所指变量a的值</span>
p = &b; <span class="hljs-comment">// 非法，指针本身的值也不能修改</span>
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="33" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="33" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E4%B8%80%E7%BB%B4%E6%95%B0%E7%BB%84%E5%8F%82%E6%95%B0%E7%9A%84%E6%8C%87%E9%92%88%E8%A1%A8%E7%A4%BA">一维数组参数的指针表示</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">sort</span><span class="hljs-params">(<span class="hljs-type">int</span> a[], <span class="hljs-type">int</span> n)</span> { ... } <span class="hljs-comment">// 等价于 void sort(int *a, int n)</span>
</code></pre>
<ul>
<li>形参
<ul>
<li>不指定长度的数组</li>
<li>即<strong>指针变量</strong></li>
</ul>
</li>
<li>实参
<ul>
<li>数组名（指针常量）</li>
<li>数组元素地址</li>
<li>指向数组元素的指针变量</li>
</ul>
</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="34" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="34" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%86%92%E6%B3%A1%E6%8E%92%E5%BA%8F%E7%A4%BA%E4%BE%8B%E6%95%B0%E7%BB%84">冒泡排序示例——数组</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">include</span><span class="hljs-string"><stdio.h></span></span>
<span class="hljs-meta">#<span class="hljs-keyword">define</span> N 10</span>
<span class="hljs-type">void</span> <span class="hljs-title function_">BubbleSort</span><span class="hljs-params">(<span class="hljs-type">int</span> *a, <span class="hljs-type">int</span> n)</span> { <span class="hljs-comment">// 形参为指针</span>
<span class="hljs-type">int</span> i, j, t;
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">1</span>; i < n; i++) <span class="hljs-comment">// 共进行n-1轮"冒泡"</span>
<span class="hljs-keyword">for</span>(j = <span class="hljs-number">0</span>; j < n - i; j++) <span class="hljs-comment">// 对两两相邻的元素进行比较</span>
<span class="hljs-keyword">if</span>(a[j] > a[j + <span class="hljs-number">1</span>]) {
t = a[j]; a[j] = a[j + <span class="hljs-number">1</span>]; a[j + <span class="hljs-number">1</span>] = t;
}
}
<span class="hljs-type">int</span> <span class="hljs-title function_">main</span><span class="hljs-params">()</span> {
<span class="hljs-type">int</span> x[N], i;
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"please input %d numbers:\n"</span>, N);
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < N; i++) <span class="hljs-built_in">scanf</span>(<span class="hljs-string">"%d"</span>, &x[i]);
BubbleSort(x, N); <span class="hljs-comment">// 实参为数组名</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"the sorted numbers:\n"</span>);
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < N; i++) <span class="hljs-built_in">printf</span>(<span class="hljs-string">"%d "</span>, x[i]);
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="35" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="35" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%86%92%E6%B3%A1%E6%8E%92%E5%BA%8F%E7%A4%BA%E4%BE%8B%E6%8C%87%E9%92%88">冒泡排序示例——指针</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">include</span><span class="hljs-string"><stdio.h></span></span>
<span class="hljs-meta">#<span class="hljs-keyword">define</span> N 10</span>
<span class="hljs-type">void</span> <span class="hljs-title function_">BubbleSort</span><span class="hljs-params">(<span class="hljs-type">int</span> *a, <span class="hljs-type">int</span> n)</span> { <span class="hljs-comment">// 形参为指针</span>
<span class="hljs-type">int</span> i, j, t;
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">1</span>; i < n; i++) <span class="hljs-comment">// 共进行n-1轮"冒泡"</span>
<span class="hljs-keyword">for</span>(j = <span class="hljs-number">0</span>; j < n - i; j++) <span class="hljs-comment">// 对两两相邻的元素进行比较</span>
<span class="hljs-keyword">if</span>(*(a+j) > *(a+j+<span class="hljs-number">1</span>)) { <span class="hljs-comment">// 改为指针实现</span>
t = *(a+j); *(a+j) = *(a+j+<span class="hljs-number">1</span>); *(a+j+<span class="hljs-number">1</span>) = t;
}
}
<span class="hljs-type">int</span> <span class="hljs-title function_">main</span><span class="hljs-params">()</span> {
<span class="hljs-type">int</span> x[N], i, *p = x;
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"please input %d numbers:\n"</span>, N);
<span class="hljs-keyword">for</span>(i=<span class="hljs-number">0</span>; i<N; i++) <span class="hljs-built_in">scanf</span>(<span class="hljs-string">"%d"</span>, &x[i]);
BubbleSort(p, N); <span class="hljs-comment">// 实参为指针变量 </span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"the sorted numbers:\n"</span>);
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < N; i++) <span class="hljs-built_in">printf</span>(<span class="hljs-string">"%d "</span>, x[i]);
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="36" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="36" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E9%AB%98%E7%B2%BE%E5%BA%A6%E8%AE%A1%E7%AE%97---%E8%B6%85%E5%A4%A7%E6%95%B4%E6%95%B0%E7%9A%84%E5%8A%A0%E6%B3%95">高精度计算 - 超大整数的加法</h2>
<h3 id="%E9%AB%98%E7%B2%BE%E5%BA%A6%E8%BF%90%E7%AE%97%E6%A6%82%E5%BF%B5">高精度运算概念</h3>
<p>高精度运算：是指参与运算的数范围大大超出了标准数据类型能表示的范围的运算。</p>
<p>例如：求两个100位的数的和，计算100!。</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="37" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="37" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h3 id="%E9%AB%98%E7%B2%BE%E5%BA%A6%E8%AE%A1%E7%AE%97%E8%A7%A3%E5%86%B3%E7%9A%84%E9%97%AE%E9%A2%98">高精度计算解决的问题</h3>
<ol>
<li><strong>大数据存储</strong></li>
<li><strong>运算过程</strong></li>
<li><strong>大数据的输入和输出</strong></li>
</ol>
<p><strong>存储</strong>：用数组存储，每个数组元素存储1位</p>
<ul>
<li>个位在<code>x[0]</code>，十位在<code>x[1]</code>，...</li>
<li>优点：每一位都是数的形式，可以直接加减，方便处理</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="38" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="38" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h3 id="%E5%A4%A7%E6%95%B0%E8%AE%A1%E7%AE%97%E6%A1%86%E6%9E%B6">大数计算框架</h3>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">define</span> N 200 <span class="hljs-comment">// 定义数位上限</span></span>
<span class="hljs-type">int</span> <span class="hljs-title function_">main</span><span class="hljs-params">(<span class="hljs-type">void</span>)</span> {
<span class="hljs-type">int</span> x[N+<span class="hljs-number">1</span>], y[N+<span class="hljs-number">1</span>], z[N+<span class="hljs-number">2</span>];
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"输入被加数："</span>);
getBigNum(x, N);
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"输入加数："</span>);
getBigNum(y, N);
addBigNum(x, y, z); <span class="hljs-comment">// z=x+y</span>
putBigNum(z);
<span class="hljs-built_in">putchar</span>(<span class="hljs-string">'\n'</span>);
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="39" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="39" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h3 id="%E8%BE%93%E5%85%A5%E5%87%BD%E6%95%B0getbignum">输入函数getBigNum</h3>
<ul>
<li>函数功能：输入一个大整数，放于数组中</li>
<li>函数参数：存放大整数的数组<code>x</code>，能输入的最多位数<code>lim</code></li>
<li>函数返回值：<code>void</code></li>
</ul>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">getBigNum</span><span class="hljs-params">(<span class="hljs-type">int</span> *x, <span class="hljs-type">int</span> lim)</span>;
</code></pre>
<ul>
<li>输入用字符一位一位输入，先输入高位再输入低位</li>
<li>实际存储：低位在低地址（也可以低位在高地址）</li>
<li>反转数组元素：个位在<code>x[1]</code>，十位在<code>x[2]</code>，...，<code>x[0]</code>放总位数</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="40" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="40" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">getBigNum</span><span class="hljs-params">(<span class="hljs-type">int</span> *x, <span class="hljs-type">int</span> lim)</span> {
<span class="hljs-type">int</span> i, t;
<span class="hljs-type">int</span> c; <span class="hljs-comment">// 存储读取的字符</span>
<span class="hljs-type">int</span> *p1, *p2; <span class="hljs-comment">// 反转数组用的指针</span>
<span class="hljs-comment">// 1. 清空数组（x[1]到x[lim-1]），避免残留垃圾值</span>
<span class="hljs-keyword">for</span> (i = <span class="hljs-number">1</span>; i < lim; i++) {
*(x + i) = <span class="hljs-number">0</span>;
}
<span class="hljs-comment">// 2. 读取用户输入的数字字符，暂存为高位在前（x[1]存最高位，x[n]存个位）</span>
i = <span class="hljs-number">1</span>;
<span class="hljs-keyword">while</span> ((c = getchar()) != EOF && <span class="hljs-built_in">isdigit</span>(c) && i < lim) { <span class="hljs-comment">// 限制不超过最大位数</span>
*(x + i) = c - <span class="hljs-string">'0'</span>; <span class="hljs-comment">// 字符转数字（'0'的ASCII码是48，减去后得到对应数字）</span>
i++;
}
*(x + <span class="hljs-number">0</span>) = i - <span class="hljs-number">1</span>; <span class="hljs-comment">// x[0]记录实际读取的位数</span>
<span class="hljs-comment">// 3. 反转数组，转为低位在前（x[1]存个位，x[n]存最高位）</span>
p1 = x + <span class="hljs-number">1</span>; <span class="hljs-comment">// 指向第一个数字（原最高位）</span>
p2 = x + (i - <span class="hljs-number">1</span>); <span class="hljs-comment">// 指向最后一个数字（原个位）</span>
<span class="hljs-keyword">while</span> (p1 < p2) { <span class="hljs-comment">// 双指针交换，直到相遇</span>
t = *p1;
*p1 = *p2;
*p2 = t;
p1++;
p2--;
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="41" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="41" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E8%BE%93%E5%87%BA%E5%87%BD%E6%95%B0putbignum">输出函数putBigNum</h2>
<p>从高位按运算结果的实际位数输出每一位（数组元素）</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">putBigNum</span><span class="hljs-params">(<span class="hljs-type">int</span> *x)</span> {
<span class="hljs-type">int</span> *p;
<span class="hljs-type">int</span> n = *x; <span class="hljs-comment">// n = x[0]，即大整数的位数</span>
<span class="hljs-keyword">for</span>(p = x + n; p > x; p--) { <span class="hljs-comment">// p从x[n]（最高位）开始，递减到x[1]（个位）</span>
<span class="hljs-built_in">printf</span>(<span class="hljs-string">"%d"</span>, *p); <span class="hljs-comment">// 依次输出每一位数字</span>
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="42" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="42" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E8%BF%90%E7%AE%97%E8%BF%87%E7%A8%8B">运算过程</h2>
<p>模拟列竖式计算两数相加（如45+96）</p>
<ol>
<li><strong>运算顺序</strong>：从低位向高位运算；先低位后高位</li>
<li><strong>运算规则</strong>：相同位的两个数相加再加上进位，成为该位的和；这个和去掉向高位的进位就成为该位的值（<code>5+6=11，11/10=1，11%10=1</code>）</li>
<li><strong>最后一位的进位</strong>：如果完成两个数的相加后，进位位值不为0，则应添加一位（<code>14+9+1=14，14/10=1，14%10=4</code>）</li>
<li><strong>位数不同</strong>：按位数多的一个进行计算</li>
</ol>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="43" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="43" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%87%BD%E6%95%B0addbignum">函数addBigNum</h2>
<ul>
<li>函数功能：两个大整数相加</li>
<li>函数参数：
<ul>
<li>输入 x--被加数，y--加数</li>
<li>输出 z--和</li>
</ul>
</li>
<li>函数返回值：void</li>
</ul>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">addBigNum</span><span class="hljs-params">(<span class="hljs-type">int</span> *z, <span class="hljs-type">int</span> *x, <span class="hljs-type">int</span> *y)</span>;
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="44" data-marpit-scope-tO56kWge="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="44" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108"><div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-comment">// 大整数加法：z = x + y（x、y、z均为“低位在前、x[0]存位数”的结构）</span>
<span class="hljs-type">void</span> <span class="hljs-title function_">addBigNum</span><span class="hljs-params">(<span class="hljs-type">int</span> *z, <span class="hljs-type">int</span> *x, <span class="hljs-type">int</span> *y)</span> {
<span class="hljs-type">int</span> i, carry, n;
<span class="hljs-comment">// 1. 和数组z先清零</span>
n = max(*x, *y); <span class="hljs-comment">// n是x、y中较长的位数</span>
<span class="hljs-keyword">for</span> (i = <span class="hljs-number">1</span>; i <= n + <span class="hljs-number">1</span>; i++) { <span class="hljs-comment">// 预留一位进位空间</span>
*(z + i) = <span class="hljs-number">0</span>;
}
<span class="hljs-comment">// 2. 带进位加法</span>
carry = <span class="hljs-number">0</span>;
<span class="hljs-keyword">for</span> (i = <span class="hljs-number">1</span>; i <= n; i++) {
<span class="hljs-comment">// 取x、y的第i位（低位），不足则补0</span>
<span class="hljs-type">int</span> x_bit = (i <= *x) ? *(x + i) : <span class="hljs-number">0</span>;
<span class="hljs-type">int</span> y_bit = (i <= *y) ? *(y + i) : <span class="hljs-number">0</span>;
*(z + i) = x_bit + y_bit + carry;
carry = *(z + i) / <span class="hljs-number">10</span>; <span class="hljs-comment">// 计算进位</span>
*(z + i) = *(z + i) % <span class="hljs-number">10</span>; <span class="hljs-comment">// 计算本位值</span>
}
<span class="hljs-comment">// 3. 处理最后的进位</span>
<span class="hljs-keyword">if</span> (carry) {
i++;
*(z + i) = carry;
}
<span class="hljs-comment">// 4. z[0]存储和的实际位数</span>
*z = i - <span class="hljs-number">1</span>;
}
</code></pre>
</div>
<div>
<p><img src="images/c-pointer-addbignum.svg" alt="" style="width:500px;" /></p>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="45" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="45" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%88%86%E6%B2%BB%E6%B3%95%E9%AB%98%E7%B2%BE%E5%BA%A6%E8%AE%A1%E7%AE%97">分治法高精度计算</h2>
<p><strong>分治法</strong>: "分而治之"就是把一个复杂的问题分成两个或更多的相同或相似的子问题，再把子问题分成更小的子问题，直到最后子问题可以简单的直接求解，原问题的解即子问题的解的合并。</p>
<p><strong>分治策略</strong>: 将"一个大数分为多个1位整数（0~9）"</p>
<p><strong>存在问题</strong>:</p>
<ol>
<li>浪费空间：整型数组的每个元素只存放一位</li>
<li>浪费时间：一次加法只处理一位</li>
</ol>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="46" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="46" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E4%BC%98%E5%8C%96%E7%AD%96%E7%95%A5">优化策略</h2>
<p>扩大<strong>粒度</strong></p>
<ol>
<li>分治策略：将"一个大数分为多个4位整数（0~9999）"</li>
<li>一个数组元素存放四位数；将标准数组改为紧缩数组</li>
<li>运算时：逢万进位；将"十进制运算"改为"万进制运算"</li>
<li>输出时：最高位直接输出，其余各位要判断是否足够4位，不足部分要补0</li>
</ol>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="47" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="47" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%80%9D%E8%80%83%E7%BB%83%E4%B9%A0">思考练习</h2>
<p>编程计算n!（n可达100）</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="48" data-marpit-scope-oYIY3MYP="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="48" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E5%92%8C%E5%AD%97%E7%AC%A6%E4%B8%B2">指针和字符串</h2>
<p><a href="#%E6%8C%87%E9%92%88%E7%9A%84%E6%A6%82%E5%BF%B5">指针的概念</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%8F%82%E6%95%B0">指针参数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E4%B8%80%E7%BB%B4%E6%95%B0%E7%BB%84">指针和一维数组</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E5%AD%97%E7%AC%A6%E4%B8%B2"><strong>指针和字符串</strong></a><br />
<a href="#%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84">指针数组</a><br />
<a href="#%E5%B8%A6%E5%8F%82%E6%95%B0%E7%9A%84main%E5%87%BD%E6%95%B0">带参数的main函数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%87%BD%E6%95%B0">指针函数</a><br />
<a href="#%E5%87%BD%E6%95%B0%E7%9A%84%E6%8C%87%E9%92%88">函数的指针</a><br />
<a href="#%E6%8C%87%E9%92%88%E4%B8%8E%E4%BA%8C%E7%BB%B4%E6%95%B0%E7%BB%84">指针与二维数组</a><br />
<a href="#%E7%94%A8typedef%E5%AE%9A%E4%B9%89%E7%B1%BB%E5%9E%8B">用typedef定义类型</a><br />
<a href="#%E5%A4%8D%E6%9D%82%E5%A3%B0%E6%98%8E">复杂声明</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="49" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="49" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%AD%97%E7%AC%A6%E4%B8%B2%E7%9A%84%E6%8C%87%E9%92%88%E8%A1%A8%E7%A4%BA">字符串的指针表示</h2>
<p>字符串是一维字符数组，要访问和操纵字符串，可以用<strong>字符数组</strong>，也可用<strong>字符指针</strong>。</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-comment">// (1) 声明字符指针变量和字符数组</span>
<span class="hljs-type">char</span> s[<span class="hljs-number">80</span>] = <span class="hljs-string">"This is a string."</span>;
<span class="hljs-type">char</span> *p = s;
<span class="hljs-built_in">puts</span>(p); <span class="hljs-comment">// 输出：This is a string.</span>
<span class="hljs-built_in">putchar</span>(*p); <span class="hljs-comment">// 输出：T</span>
s = <span class="hljs-string">"This is a book."</span>; <span class="hljs-comment">// 错，数组名s是指针常量</span>
<span class="hljs-built_in">strcpy</span>(s, <span class="hljs-string">"This is a string."</span>); <span class="hljs-comment">// √</span>
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="50" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="50" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%AD%97%E7%AC%A6%E4%B8%B2%E7%9A%84%E6%8C%87%E9%92%88%E8%A1%A8%E7%A4%BA%E7%BB%AD">字符串的指针表示(续)</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-comment">// (2) 声明和初始化字符指针变量</span>
<span class="hljs-type">char</span> *p = <span class="hljs-string">"This is a string."</span>;
<span class="hljs-comment">/* 分配内存给字符指针p；
分配内存给字符串常量（只读）；
将字符串首地址赋值给字符指针； */</span>
<span class="hljs-built_in">puts</span>(p); <span class="hljs-comment">// 输出 This is a string.</span>
<span class="hljs-built_in">putchar</span>(p[<span class="hljs-number">1</span>]); <span class="hljs-comment">// 输出 h</span>
p = <span class="hljs-string">"This is a book."</span>; <span class="hljs-comment">// √, p是指针变量, 不提倡</span>
*p = <span class="hljs-string">'t'</span>; <span class="hljs-comment">// 运行错</span>
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="51" data-marpit-scope-FslrECZu="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="51" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E5%AD%97%E7%AC%A6%E4%B8%B2%E4%BD%9C%E5%87%BD%E6%95%B0%E5%8F%82%E6%95%B0">字符串作函数参数</h2>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">mystrcpy</span><span class="hljs-params">(<span class="hljs-type">char</span> *t, <span class="hljs-type">const</span> <span class="hljs-type">char</span> *s)</span> {
<span class="hljs-keyword">while</span>( (*t=*s) != ˊ\<span class="hljs-number">0</span>ˊ )
t++,s++;
}
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">mystrcpy</span><span class="hljs-params">(<span class="hljs-type">char</span> *t, <span class="hljs-type">const</span> <span class="hljs-type">char</span> *s)</span> {
<span class="hljs-keyword">while</span>((*t++ = *s++) != <span class="hljs-string">'\0'</span>);
} <span class="hljs-comment">// 简化</span>
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">void</span> <span class="hljs-title function_">mystrcpy</span><span class="hljs-params">(<span class="hljs-type">char</span> *t, <span class="hljs-type">const</span> <span class="hljs-type">char</span> *s)</span> {
<span class="hljs-keyword">while</span>(*t++=*s++);
} <span class="hljs-comment">// 完全简化</span>
</code></pre>
</div>
<div>
<p>使用注意</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">char</span> t[<span class="hljs-number">30</span>], s[] = <span class="hljs-string">"world"</span>;
<span class="hljs-type">char</span> *p;
mystrcpy(t, <span class="hljs-string">"hello"</span>); <span class="hljs-comment">// √</span>
mystrcpy(t, s); <span class="hljs-comment">// √</span>
mystrcpy(p, s); <span class="hljs-comment">// ×</span>
p = t;
mystrcpy(p, s); <span class="hljs-comment">// √</span>
</code></pre>
</div>
</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="52" data-marpit-scope-j66SLmHq="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="52" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84">指针数组</h2>
<p><a href="#%E6%8C%87%E9%92%88%E7%9A%84%E6%A6%82%E5%BF%B5">指针的概念</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%8F%82%E6%95%B0">指针参数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E4%B8%80%E7%BB%B4%E6%95%B0%E7%BB%84">指针和一维数组</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%92%8C%E5%AD%97%E7%AC%A6%E4%B8%B2">指针和字符串</a><br />
<a href="#%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84"><strong>指针数组</strong></a><br />
<a href="#%E5%B8%A6%E5%8F%82%E6%95%B0%E7%9A%84main%E5%87%BD%E6%95%B0">带参数的main函数</a><br />
<a href="#%E6%8C%87%E9%92%88%E5%87%BD%E6%95%B0">指针函数</a><br />
<a href="#%E5%87%BD%E6%95%B0%E7%9A%84%E6%8C%87%E9%92%88">函数的指针</a><br />
<a href="#%E6%8C%87%E9%92%88%E4%B8%8E%E4%BA%8C%E7%BB%B4%E6%95%B0%E7%BB%84">指针与二维数组</a><br />
<a href="#%E7%94%A8typedef%E5%AE%9A%E4%B9%89%E7%B1%BB%E5%9E%8B">用typedef定义类型</a><br />
<a href="#%E5%A4%8D%E6%9D%82%E5%A3%B0%E6%98%8E">复杂声明</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="53" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="53" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84%E5%AE%9A%E4%B9%89">指针数组定义</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-type">int</span> *p[<span class="hljs-number">3</span>]; <span class="hljs-comment">// p是一个有3个元素的整型指针数组</span>
<span class="hljs-comment">// 即每个元素是指向整型变量的指针</span>
<span class="hljs-type">char</span> *ps[<span class="hljs-number">2</span>] = {<span class="hljs-string">"red"</span>, <span class="hljs-string">"green"</span>}; <span class="hljs-comment">// ps是一个有2个元素的字符指针数组</span>
<span class="hljs-comment">// ps[0]指向字符串"red"</span>
<span class="hljs-comment">// ps[1]指向字符串"green"</span>
<span class="hljs-type">const</span> <span class="hljs-type">char</span> *ps[<span class="hljs-number">2</span>] = {<span class="hljs-string">"red"</span>, <span class="hljs-string">"green"</span>}; <span class="hljs-comment">// 只用不改</span>
</code></pre>
<p><img src="images/c-pointer-array.svg" alt="" style="height:200px;" /></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="54" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="54" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h2 id="%E6%8C%87%E9%92%88%E6%95%B0%E7%BB%84%E7%9A%84%E5%BA%94%E7%94%A8">指针数组的应用</h2>
<ul>
<li>描述二维数组
<ul>
<li>数值型二维数组</li>
<li>字符型二维数组 (字符串数组)</li>
</ul>
</li>
<li>尤其是
<ul>
<li>每行元素个数不相同的二维数组，如:
<ul>
<li>三角矩阵</li>
<li>图结构数据 (邻接表)</li>
<li>不同长度的字符串组成的字符串数组</li>
</ul>
</li>
</ul>
</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="55" data-marpit-scope-50mKTgY1="" data-paginate="true" data-theme="gaia" lang="zh-CN" data-marpit-pagination="55" style="--paginate:true;--theme:gaia;" data-marpit-pagination-total="108">
<h3 id="%E6%9D%A8%E8%BE%89%E4%B8%89%E8%A7%92%E5%BD%A2">杨辉三角形</h3>
<div class="columns">
<div>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">define</span> N 5</span>
<span class="hljs-meta">#<span class="hljs-keyword">define</span> SIZE N*(N+1)/2</span>
<span class="hljs-type">int</span> <span class="hljs-title function_">main</span><span class="hljs-params">()</span>
{
<span class="hljs-type">int</span> *p[N], a[SIZE];
<span class="hljs-type">int</span> sum = <span class="hljs-number">0</span>, i;
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < N; i++) { <span class="hljs-comment">// p[i]指向各行首元素</span>
p[i] = &a[sum]; <span class="hljs-comment">// a[0], a[1], ..., a[i*(i+1)/2]</span>
sum += i + <span class="hljs-number">1</span>;
}
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < N; i++) { <span class="hljs-comment">// 遍历各行</span>
*p[i] = <span class="hljs-number">1</span>; <span class="hljs-comment">// 初始化行首元素为1</span>
*(p[i] + i) = <span class="hljs-number">1</span>; <span class="hljs-comment">// 初始化行尾元素为1</span>
}
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">2</span>; i < N; i++) <span class="hljs-comment">// 填充内部三角</span>
<span class="hljs-keyword">for</span>(k = <span class="hljs-number">1</span>; k < i; k++)
p[i][k] = p[i<span class="hljs-number">-1</span>][k<span class="hljs-number">-1</span>] + p[i<span class="hljs-number">-1</span>][k]; <span class="hljs-comment">// 引用上一行元素计算</span>
<span class="hljs-keyword">return</span> <span class="hljs-number">0</span>;
}
</code></pre>
</div>
<div>
<p><img src="images/c-pointer-yanghui.svg" alt="" style="width:330px;" /><br />
用指针运算快速定位数组元素首地址</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-c"> <span class="hljs-type">int</span> *a_ptr = a;
<span class="hljs-keyword">for</span>(i = <span class="hljs-number">0</span>; i < N; i++) {
p[i] = a_ptr;
a_ptr += (i + <span class="hljs-number">1</span>);
}
</code></pre>
</div>
</div>
</section>