man3/toupper.3

   1 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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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  2017-09-15 "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 .BI "int tolower(int " "c" );
  37 .PP
  38 .BI "int toupper_l(int " c ", locale_t " locale );
  39 .BI "int tolower_l(int " c ", locale_t " locale );
  40 .fi
  41 .PP
  42 .in -4n
  43 Feature Test Macro Requirements for glibc (see
  44 .BR feature_test_macros (7)):
  45 .in
  46 .PP
  47 .BR toupper_l (),
  48 .BR tolower_l ():
  49 .PD 0
  50 .RS 4
  51 .TP
  52 Since glibc 2.10:
  53 _XOPEN_SOURCE\ >=\ 700
  54 .TP
  55 Before glibc 2.10:
  56 _GNU_SOURCE
  57 .RE
  58 .PD
  59 .SH DESCRIPTION
  60 These functions convert lowercase letters to uppercase, and vice versa.
  61 .PP
  62 If
  63 .I c
  64 is a lowercase letter,
  65 .BR toupper ()
  66 returns its uppercase equivalent,
  67 if an uppercase representation exists in the current locale.
  68 Otherwise, it returns
  69 .IR c .
  70 The
  71 .BR toupper_l ()
  72 function performs the same task,
  73 but uses the locale referred to by the locale handle
  74 .IR locale .
  75 .PP
  76 If
  77 .I c
  78 is an uppercase letter,
  79 .BR tolower ()
  80 returns its lowercase equivalent,
  81 if a lowercase representation exists in the current locale.
  82 Otherwise, it returns
  83 .IR c .
  84 The
  85 .BR tolower_l ()
  86 function performs the same task,
  87 but uses the locale referred to by the locale handle
  88 .IR locale .
  89 .PP
  90 If
  91 .I c
  92 is neither an
  93 .I "unsigned char"
  94 value nor
  95 .BR EOF ,
  96 the behavior of these functions
  97 is undefined.
  98 .PP
  99 The behavior of
 100 .BR toupper_l ()
 101 and
 102 .BR tolower_l ()
 103 is undefined if
 104 .I locale
 105 is the special locale object
 106 .BR LC_GLOBAL_LOCALE
 107 (see
 108 .BR duplocale (3))
 109 or is not a valid locale object handle.
 110 .SH RETURN VALUE
 111 The value returned is that of the converted letter, or
 112 .I c
 113 if the conversion was not possible.
 114 .SH ATTRIBUTES
 115 For an explanation of the terms used in this section, see
 116 .BR attributes (7).
 117 .TS
 118 allbox;
 119 lbw24 lb lb
 120 l l l.
 121 Interface       Attribute       Value
 122 T{
 123 .BR toupper (),
 124 .BR tolower (),
 125 .br
 126 .BR toupper_l (),
 127 .BR tolower_l ()
 128 T}      Thread safety   MT-Safe
 129 .TE
 130 .SH CONFORMING TO
 131 .BR toupper (),
 132 .BR tolower ():
 133 C89, C99, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
 134 .PP
 135 .BR toupper_l (),
 136 .BR tolower_l ():
 137 POSIX.1-2008.
 138 .SH NOTES
 139 The standards require that the argument
 140 .I c
 141 for these functions is either
 142 .B EOF
 143 or a value that is representable in the type
 144 .IR "unsigned char" .
 145 If the argument
 146 .I c
 147 is of type
 148 .IR char ,
 149 it must be cast to
 150 .IR "unsigned char" ,
 151 as in the following example:
 152 .PP
 153 .in +4n
 154 .EX
 155 char c;
 156 \&...
 157 res = toupper((unsigned char) c);
 158 .EE
 159 .in
 160 .PP
 161 This is necessary because
 162 .I char
 163 may be the equivalent
 164 .IR "signed char" ,
 165 in which case a byte where the top bit is set would be sign extended when
 166 converting to
 167 .IR int ,
 168 yielding a value that is outside the range of
 169 .IR "unsigned char" .
 170 .PP
 171 The details of what constitutes an uppercase or lowercase letter depend
 172 on the locale.
 173 For example, the default
 174 .B """C"""
 175 locale does not know about umlauts, so no conversion is done for them.
 176 .PP
 177 In some non-English locales, there are lowercase letters with no
 178 corresponding uppercase equivalent;
 179 .\" FIXME One day the statement about "sharp s" needs to be reworked,
 180 .\" since there is nowadays a capital "sharp s" that has a codepoint
 181 .\" in Unicode 5.0; see https://en.wikipedia.org/wiki/Capital_%E1%BA%9E
 182 the German sharp s is one example.
 183 .SH SEE ALSO
 184 .BR isalpha (3),
 185 .BR newlocale (3),
 186 .BR setlocale (3),
 187 .BR towlower (3),
 188 .BR towupper (3),
 189 .BR uselocale (3),
 190 .BR locale (7)