toupper(3) - Linux manual page (original) (raw)

toupper(3) Library Functions Manual toupper(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(int** _c_**);**
   **int tolower(int** _c_**);**

   **int toupper_l(int** _c_**, locale_t** _locale_**);**
   **int tolower_l(int** _c_**, locale_t** _locale_**);**

Feature Test Macro Requirements for glibc (see feature_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.

   If _c_ is a lowercase letter, **toupper**() returns its uppercase
   equivalent, if an uppercase representation exists in the current
   locale.  Otherwise, it returns _c_.  The **toupper_l**() function
   performs the same task, but uses the locale referred to by the
   locale handle _locale_.

   If _c_ is an uppercase letter, **tolower**() returns its lowercase
   equivalent, if a lowercase representation exists in the current
   locale.  Otherwise, it returns _c_.  The **tolower_l**() function
   performs the same task, but uses the locale referred to by the
   locale handle _locale_.

   If _c_ is neither an _unsigned char_ value nor **EOF**, the behavior of
   these functions is undefined.

   The behavior of **toupper_l**() and **tolower_l**() is undefined if _locale_
   is the special locale object **LC_GLOBAL_LOCALE** (see [duplocale(3)](../man3/duplocale.3.html))
   or is not a valid locale object handle.

RETURN VALUE top

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

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **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 argument _c_ for these functions is
   either **EOF** or a value that is representable in the type _unsigned_
   _char_.  If the argument _c_ is of type _char_, it must be cast to
   _unsigned char_, as in the following example:

       char c;
       ...
       res = toupper((unsigned char) c);

   This is necessary because _char_ may be the equivalent _signed char_,
   in which case a byte where the top bit is set would be sign
   extended when converting to _int_, yielding a value that is outside
   the range of _unsigned 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)](../man3/isalpha.3.html), [newlocale(3)](../man3/newlocale.3.html), [setlocale(3)](../man3/setlocale.3.html), [towlower(3)](../man3/towlower.3.html), [towupper(3)](../man3/towupper.3.html),
   [uselocale(3)](../man3/uselocale.3.html), [locale(7)](../man7/locale.7.html)

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Linux man-pages 6.10 2024-07-23 toupper(3)

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