ctype.h File Reference

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Functions
Character classification routines
These functions perform character classification. They return true or false status depending whether the character passed to the function falls into the function's classification (i.e. isdigit() returns true if its argument is any value '0' though '9', inclusive). If the input is not an unsigned char value, all of this function return false.
int	isalnum (int __c)
int	isalpha (int __c)
int	isascii (int __c)
int	isblank (int __c)
int	iscntrl (int __c)
int	isdigit (int __c)
int	isgraph (int __c)
int	islower (int __c)
int	isprint (int __c)
int	ispunct (int __c)
int	isspace (int __c)
int	isupper (int __c)
int	isxdigit (int __c)
Character convertion routines
This realization permits all possible values of integer argument. The toascii() function clears all highest bits. The tolower() and toupper() functions return an input argument as is, if it is not an unsigned char value.
int	toascii (int __c)
int	tolower (int __c)
int	toupper (int __c)