P1892R1 Extended locale-specific presentation specifiers for std::format

Also fixes NB GB 226 (C++20 CD).

Author: Dawn Perchik

source/utilities.tex

@@ -19682,7 +19682,7 @@
 
 \begin{ncbnf}
 \fmtnontermdef{std-format-spec}\br
-    \opt{fill-and-align} \opt{sign} \opt{\terminal{\#}} \opt{\terminal{0}} \opt{width} \opt{precision} \opt{type}
+    \opt{fill-and-align} \opt{sign} \opt{\terminal{\#}} \opt{\terminal{0}} \opt{width} \opt{precision} \opt{\terminal{L}} \opt{type}
 \end{ncbnf}
 
 \begin{ncbnf}
@@ -19719,7 +19719,7 @@
 
 \begin{ncbnf}
 \fmtnontermdef{type} \textnormal{one of}\br
-    \terminal{a A b B c d e E f F g G n o p s x X}
+    \terminal{a A b B c d e E f F g G o p s x X}
 \end{ncbnf}
 
 \pnum
@@ -19880,6 +19880,22 @@
 For floating-point types this field specifies the formatting precision.
 For string types it specifies how many characters will be used from the string.
 
+\pnum
+The \tcode{L} option causes
+the \defnx{locale-specific form}{locale-specific form!format string}
+to be used for the conversion.
+This option is only valid for arithmetic types.
+For integral types, the locale-specific form
+causes the context's locale to be used
+to insert the appropriate digit group separator characters.
+For floating-point types, the locale-specific form
+causes the context's locale to be used
+to insert the appropriate digit group and decimal radix separator characters.
+For the textual representation of \tcode{bool}, the locale-specific form
+causes the context's locale to be used
+to insert the appropriate string as if obtained
+with \tcode{numpunct::truename} or \tcode{numpunct::falsename}.
+
 \pnum
 The \fmtgrammarterm{type} determines how the data should be presented.
 
@@ -19919,7 +19935,7 @@
 string s0 = format("{}", 42);                           // value of \tcode{s0} is \tcode{"42"}
 string s1 = format("{0:b} {0:d} {0:o} {0:x}", 42);      // value of \tcode{s1} is \tcode{"101010 42 52 2a"}
 string s2 = format("{0:#x} {0:#X}", 42);                // value of \tcode{s2} is \tcode{"0x2a 0X2A"}
-string s3 = format("{:n}", 1234);                       // value of \tcode{s3} might be \tcode{"1,234"}
+string s3 = format("{:L}", 1234);                       // value of \tcode{s3} might be \tcode{"1,234"}
                                                         // (depending on the locale)
 \end{codeblock}
 \end{example}
@@ -19968,12 +19984,6 @@
 the base prefix is \tcode{0X}.
 \\ \rowsep
 %
-\tcode{n} &
-The same as \tcode{d}, except that
-it uses the context's locale
-to insert the appropriate digit group separator characters.
-\\ \rowsep
-%
 none &
 The same as \tcode{d}.
 \begin{note}
@@ -19993,7 +20003,7 @@
 Copies the character to the output.
 \\ \rowsep
 %
-\tcode{b}, \tcode{B}, \tcode{d}, \tcode{o}, \tcode{x}, \tcode{X}, \tcode{n} &
+\tcode{b}, \tcode{B}, \tcode{d}, \tcode{o}, \tcode{x}, \tcode{X} &
 As specified in \tref{format.type.int}.
 \\
 \end{floattable}
@@ -20009,7 +20019,7 @@
 Copies textual representation, either \tcode{true} or \tcode{false}, to the output.
 \\ \rowsep
 %
-\tcode{b}, \tcode{B}, \tcode{c}, \tcode{d}, \tcode{o}, \tcode{x}, \tcode{X}, \tcode{n} &
+\tcode{b}, \tcode{B}, \tcode{c}, \tcode{d}, \tcode{o}, \tcode{x}, \tcode{X} &
 As specified in \tref{format.type.int}
 for the value
 \tcode{static_cast<unsigned char>(value)}.
@@ -20087,12 +20097,6 @@
 it uses \tcode{E} to indicate exponent.
 \\ \rowsep
 %
-\tcode{n} &
-The same as \tcode{g}, except that
-it uses the context's locale to insert the appropriate
-digit group and decimal radix separator characters.
-\\ \rowsep
-%
 none &
 If \fmtgrammarterm{precision} is specified, equivalent to
 \begin{codeblock}