NAME
toupper, tolower - convert letter to upper or lower case SYNOPSIS
#include
int toupper(int c); int tolower(int c); DESCRIPTION toupper() converts the letter c to upper case, if possible. tolower() converts the letter c to lower case, if possible. If c is not an unsigned char value, or EOF, the behavior of these func‐ tions is undefined. RETURN VALUE The value returned is that of the converted letter, or c if the conver‐ sion was not possible. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌─────────────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├─────────────────────────┼───────────────┼─────────┤ │toupper(), tolower(), │ Thread safety │ MT-Safe │ │toupperl(), tolowerl() │ │ │ └─────────────────────────┴───────────────┴─────────┘ CONFORMING TO C89, C99, 4.3BSD. BUGS The details of what constitutes an uppercase or lowercase letter depend on the current 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 corre‐ sponding uppercase equivalent; the German sharp s is one example. SEE ALSO isalpha(3), setlocale(3), towlower(3), towupper(3), locale(7) COLOPHON
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GNU 1993-04-04 TOUPPER(3)