toupper, tolower - convert letter to upper or lower case
int toupper(int c);
int tolower(int c);
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 functions is undefined.
The value returned is that of the converted letter, or c if the conversion was not possible.
C89, C99, 4.3BSD.
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 corresponding uppercase equivalent; the German sharp s is one example.
isalpha(3), setlocale(3), towlower(3), towupper(3), locale(7)
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.