man3/toupper.3

   1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
   2 .\" and Copyright 2014 Michael Kerrisk <mtk.manpages@gmail.com>
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  26 .\" Modified Sat Jul 24 17:45:39 1993 by Rik Faith (faith@cs.unc.edu)
  27 .\" Modified 2000-02-13 by Nicolás Lichtmaier <nick@debian.org>
  28 .TH TOUPPER 3  2016-10-08 "GNU" "Linux Programmer's Manual"
  29 .SH NAME
  30 toupper, tolower, toupper_l, tolower_l \- convert uppercase or lowercase
  31 .SH SYNOPSIS
  32 .nf
  33 .B #include <ctype.h>
  34 .PP
  35 .BI "int toupper(int " "c" );
  36 .br
  37 .BI "int tolower(int " "c" );
  38 .PP
  39 .BI "int toupper_l(int " c ", locale_t " locale );
  40 .BI "int tolower_l(int " c ", locale_t " locale );
  41 .fi
  42 .PP
  43 .in -4n
  44 Feature Test Macro Requirements for glibc (see
  45 .BR feature_test_macros (7)):
  46 .in
  47 .PP
  48 .BR toupper_l (),
  49 .BR tolower_l ():
  50 .PD 0
  51 .RS 4
  52 .TP
  53 Since glibc 2.10:
  54 _XOPEN_SOURCE\ >=\ 700
  55 .TP
  56 Before glibc 2.10:
  57 _GNU_SOURCE
  58 .RE
  59 .PD
  60 .SH DESCRIPTION
  61 These functions convert lowercase letters to uppercase, and vice versa.
  62 .PP
  63 If
  64 .I c
  65 is a lowercase letter,
  66 .BR toupper ()
  67 returns its uppercase equivalent,
  68 if an uppercase representation exists in the current locale.
  69 Otherwise, it returns
  70 .IR c .
  71 The
  72 .BR toupper_l ()
  73 function performs the same task,
  74 but uses the locale referred to by the locale handle
  75 .IR locale .
  76 .PP
  77 If
  78 .I c
  79 is an uppercase letter,
  80 .BR tolower ()
  81 returns its lowercase equivalent,
  82 if a lowercase representation exists in the current locale.
  83 Otherwise, it returns
  84 .IR c .
  85 The
  86 .BR tolower_l ()
  87 function performs the same task,
  88 but uses the locale referred to by the locale handle
  89 .IR locale .
  90 .PP
  91 If
  92 .I c
  93 is neither an
  94 .I "unsigned char"
  95 value nor
  96 .BR EOF ,
  97 the behavior of these functions
  98 is undefined.
  99 .PP
 100 The behavior of
 101 .BR toupper_l ()
 102 and
 103 .BR tolower_l ()
 104 is undefined if
 105 .I locale
 106 is the special locale object
 107 .BR LC_GLOBAL_LOCALE
 108 (see
 109 .BR duplocale (3))
 110 or is not a valid locale object handle.
 111 .SH RETURN VALUE
 112 The value returned is that of the converted letter, or
 113 .I c
 114 if the conversion was not possible.
 115 .SH ATTRIBUTES
 116 For an explanation of the terms used in this section, see
 117 .BR attributes (7).
 118 .TS
 119 allbox;
 120 lbw24 lb lb
 121 l l l.
 122 Interface       Attribute       Value
 123 T{
 124 .BR toupper (),
 125 .BR tolower (),
 126 .br
 127 .BR toupper_l (),
 128 .BR tolower_l ()
 129 T}      Thread safety   MT-Safe
 130 .TE
 131 .SH CONFORMING TO
 132 .BR toupper (),
 133 .BR tolower ():
 134 C89, C99, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
 135 .PP
 136 .BR toupper_l (),
 137 .BR tolower_l ():
 138 POSIX.1-2008.
 139 .SH NOTES
 140 The standards require that the argument
 141 .I c
 142 for these functions is either
 143 .B EOF
 144 or a value that is representable in the type
 145 .IR "unsigned char" .
 146 If the argument
 147 .I c
 148 is of type
 149 .IR char ,
 150 it must be cast to
 151 .IR "unsigned char" ,
 152 as in the following example:
 153 .PP
 154 .nf
 155 .in +4n
 156 char c;
 157 \&...
 158 res = toupper((unsigned char) c);
 159 .in
 160 .fi
 161 .PP
 162 This is necessary because
 163 .I char
 164 may be the equivalent
 165 .IR "signed char" ,
 166 in which case a byte where the top bit is set would be sign extended when
 167 converting to
 168 .IR int ,
 169 yielding a value that is outside the range of
 170 .IR "unsigned char" .
 171 .PP
 172 The details of what constitutes an uppercase or lowercase letter depend
 173 on the locale.
 174 For example, the default
 175 .B """C"""
 176 locale does not know about umlauts, so no conversion is done for them.
 177 .PP
 178 In some non-English locales, there are lowercase letters with no
 179 corresponding uppercase equivalent;
 180 .\" FIXME One day the statement about "sharp s" needs to be reworked,
 181 .\" since there is nowadays a capital "sharp s" that has a codepoint
 182 .\" in Unicode 5.0; see https://en.wikipedia.org/wiki/Capital_%E1%BA%9E
 183 the German sharp s is one example.
 184 .SH SEE ALSO
 185 .BR isalpha (3),
 186 .BR newlocale (3),
 187 .BR setlocale (3),
 188 .BR towlower (3),
 189 .BR towupper (3),
 190 .BR uselocale (3),
 191 .BR locale (7)