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NAME

       toupper, tolower - convert letter to upper or lower case

SYNOPSIS

       #include <ctype.h>

       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 functions is undefined.

RETURN VALUE

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

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  corresponding  uppercase
       equivalent; the German sharp s is one example.

SEE ALSO

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

COLOPHON

       This  page  is  part of release 3.35 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
       pages/.