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toupper(3) — Linux manual page

toupper(3)               Library Functions Manualtoupper(3)

NAME        top

       toupper, tolower, toupper_l, tolower_l - convert uppercase or       lowercase

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <ctype.h>int toupper(intc);int tolower(intc);int toupper_l(intc, locale_tlocale);int tolower_l(intc, locale_tlocale);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):toupper_l(),tolower_l():           Since glibc 2.10:               _XOPEN_SOURCE >= 700           Before glibc 2.10:               _GNU_SOURCE

DESCRIPTION        top

       These functions convert lowercase letters to uppercase, and vice       versa.       Ifc is a lowercase letter,toupper() returns its uppercase       equivalent, if an uppercase representation exists in the current       locale.  Otherwise, it returnsc.  Thetoupper_l() function       performs the same task, but uses the locale referred to by the       locale handlelocale.       Ifc is an uppercase letter,tolower() returns its lowercase       equivalent, if a lowercase representation exists in the current       locale.  Otherwise, it returnsc.  Thetolower_l() function       performs the same task, but uses the locale referred to by the       locale handlelocale.       Ifc is neither anunsigned char value norEOF, the behavior of       these functions is undefined.       The behavior oftoupper_l() andtolower_l() is undefined iflocale       is the special locale objectLC_GLOBAL_LOCALE(seeduplocale(3))       or is not a valid locale object handle.

RETURN VALUE        top

       The value returned is that of the converted letter, orc if the       conversion was not possible.

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │toupper(),tolower(),toupper_l(),   │ Thread safety │ MT-Safe │       │tolower_l()                          │               │         │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS        top

toupper()tolower()              C11, POSIX.1-2008.toupper_l()tolower_l()              POSIX.1-2008.

HISTORY        top

toupper()tolower()              C89, 4.3BSD, POSIX.1-2001.toupper_l()tolower_l()              POSIX.1-2008.

NOTES        top

       The standards require that the argumentc for these functions is       eitherEOFor a value that is representable in the typeunsignedchar.  If the argumentc is of typechar, it must be cast tounsigned char, as in the following example:           char c;           ...           res = toupper((unsigned char) c);       This is necessary becausechar may be the equivalentsigned char,       in which case a byte where the top bit is set would be sign       extended when converting toint, yielding a value that is outside       the range ofunsigned char.       The details of what constitutes an uppercase or lowercase letter       depend on the locale.  For example, the default"C"locale does       not know about umlauts, so no conversion is done for them.       In some non-English locales, there are lowercase letters with no       corresponding uppercase equivalent; the German sharp s is one       example.

SEE ALSO        top

isalpha(3),newlocale(3),setlocale(3),towlower(3),towupper(3),uselocale(3),locale(7)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17toupper(3)

Pages that refer to this page:duplocale(3), isalpha(3), toascii(3), towlower(3), towupper(3), wctrans(3), locale(7)

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