3.14 toupper—translate characters to uppercase

Synopsis

     #include <ctype.h>
     int toupper(int c);
     int _toupper(int c);
     

Description
toupper is a macro which converts lowercase characters to uppercase, leaving all other characters unchanged. It is only defined when c is an integer in the range EOF to 255.

You can use a compiled subroutine instead of the macro definition by undefining this macro using `#undef toupper'.

_toupper performs the same conversion as toupper, but should only be used when c is known to be a lowercase character (a–z).

Returns
toupper returns the uppercase equivalent of c when it is a character between a and z, and c otherwise.

_toupper returns the uppercase equivalent of c when it is a character between a and z. If c is not one of these characters, the behaviour of _toupper is undefined.

Portability
toupper is ANSI C. _toupper is not recommended for portable programs.

No supporting OS subroutines are required.