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190+ 最終更新日時(UTC):
191+ < span itemprop ="datePublished " content ="2025-07-05T13:32:44 ">
192+ 2025年07月05日 13時32分44秒
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205+ </ a >
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207+ < span class ="fa fa-fw fa-pencil "> </ span > 編集
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214+
215+ < div class ="identifier-type "> function</ div > < div class ="header "> <cstdlib></ div > < h1 itemprop ="name "> < span class ="namespace " title ="namespace std "> std::</ span > < span class ="token "> atof</ span > </ h1 >
216+ < div itemprop ="articleBody "> < p > < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="kt "> double</ span > < span class ="nf "> atof</ span > < span class ="p "> (</ span > < span class ="k "> const</ span > < span class ="kt "> char</ span > < span class ="o "> *</ span > < span class ="n "> str</ span > < span class ="p "> );</ span >
217+ </ code > </ pre > </ div >
218+ </ p >
219+ < h2 > 概要</ h2 >
220+ < p > < code > str</ code > を< code > float</ code > に変換する。</ p >
221+ < h2 > 変換方法</ h2 >
222+ < ul >
223+ < li >
224+ < p > 空白文字から始まる場合、最初の非空白文字から変換する。</ p >
225+ </ li >
226+ < li >
227+ < p > < code > 0x</ code > または < code > 0X</ code > の場合、空白でない16進数として処理する。</ p >
228+ </ li >
229+ < li >
230+ < p > < code > e</ code > または< code > E</ code > は、それより前を基数、その後ろを指数として処理する。</ p >
231+ </ li >
232+ < li >
233+ < p > + 、-は変換後の符号に適用される。</ p >
234+ </ li >
235+ < li >
236+ < p > < code > INF</ code > または< code > INFINITY</ code > (大小文字区別せず)は< code > inf</ code > を返す。</ p >
237+ </ li >
238+ < li >
239+ < p > NAN(大小文字区別せず)はそれ以前の数値を返す。もし以前の数値がないなら、< code > nan</ code > を返す。</ p >
240+ </ li >
241+ </ ul >
242+ < h2 > 返り値</ h2 >
243+ < p > 変換可能ならば変換後の数値。</ p >
244+ < p > 変換後の数値が< code > float</ code > の範囲外なら、その< a class ="cpprefjp-defined-word " data-desc ="未定義の動作。処理系は予期せぬ動作をする可能性がある。要するに動作保証対象外。undefined behavior (UB)。 " href ="../../implementation-compliance.html#dfn-undefined-behavior "> 動作は未定義</ a > である。</ p >
245+ < p > 変換不能なら< code > 0.0</ code > を返す。</ p >
246+ < h2 > 例</ h2 >
247+ < p > < div class ="yata " id ="8eef66f53a10f9058349d0a12fb04c12b2ee9f21 "> < div class ="codehilite "> < pre > < span > </ span > < code > < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../cstdlib.html "> <cstdlib></ a > </ span > < span class ="cp "> </ span >
248+ < span class ="cp "> #include</ span > < span class ="cpf "> < a href ="../iostream.html "> <iostream></ a > </ span > < span class ="cp "> </ span >
249+
250+ < span class ="kt "> int</ span > < span class ="nf "> main</ span > < span class ="p "> ()</ span >
251+ < span class ="p "> {</ span >
252+ < span class ="n "> < a href ="../iostream/cout.html "> std::cout</ a > </ span > < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "0.0000000123"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span >
253+ < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "0.012"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span >
254+ < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "15e16"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span >
255+ < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "-0x1afp-2"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span >
256+ < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "inF"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span >
257+ < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "12Nan23"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span >
258+ < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "NAN"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span >
259+ < span class ="o "> <<</ span > < span class ="n "> std</ span > < span class ="o "> ::</ span > < span class ="n "> atof</ span > < span class ="p "> (</ span > < span class ="s "> "invalid"</ span > < span class ="p "> )</ span > < span class ="o "> <<</ span > < span class ="sc "> '\n'</ span > < span class ="p "> ;</ span >
260+ < span class ="p "> }</ span >
261+ </ code > </ pre > </ div >
262+ </ div > </ p >
263+ < h2 > バージョン</ h2 >
264+ < h3 > 処理系</ h3 >
265+ < ul >
266+ < li > Clang: ?</ li >
267+ < li > GCC: 13< span aria-label ="検証済 " role ="img " title ="検証済 "> ✅</ span > </ li >
268+ < li > ICC: ?</ li >
269+ < li > Visual C++</ li >
270+ </ ul >
271+ < h2 > 出力結果</ h2 >
272+ < p > < pre > < code > 1.23e-08
273+ 0.012
274+ 1.5e+17
275+ -107.75
276+ inf
277+ 12
278+ nan
279+ 0
280+ </ code > </ pre > </ p > </ div >
281+
282+ </ div >
283+ </ div >
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