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NAME

isalpha, isupper, islower, isdigit, isxdigit, isalnum, isspace, ispunct, isprint, isgraph, iscntrl, isblank, toupper, tolower, — character classification and mapping functions

LIBRARY

library “libc”

SYNOPSIS

#include <ctype.h>

isalpha(int c);

isupper(int c);

islower(int c);

isdigit(int c);

isxdigit(int c);

isalnum(int c);

isspace(int c);

ispunct(int c);

isprint(int c);

isgraph(int c);

iscntrl(int c);

isblank(int c);

toupper(int c);

tolower(int c);

EXAMPLES

To print an upper-case version of a string to stdout, the following code can be used:

const char *s = "xyz";

while (*s != '\0') {
    putchar(toupper((unsigned char)*s));
    s++;
}

SEE ALSO

isalnum(3), isalpha(3), isblank(3), iscntrl(3), isdigit(3), isgraph(3), islower(3), isprint(3), ispunct(3), isspace(3), isupper(3), isxdigit(3), tolower(3), toupper(3), ascii(7)

STANDARDS

These functions, with the exception of isblank(), conform to ANSI X3.159-1989 (“ANSI C89”). All described functions, including isblank(), also conform to IEEE Std 1003.1-2001 (“POSIX.1”).

CAVEATS

The first argument of these functions is of type int, but only a very restricted subset of values are actually valid. The argument must either be the value of the macro EOF (which has a negative value), or must be a non-negative value within the range representable as unsigned char. Passing invalid values leads to undefined behavior.

Values of type int that were returned by getc(3), fgetc(3), and similar functions or macros are already in the correct range, and may be safely passed to these ctype functions without any casts.

Values of type char or signed char must first be cast to unsigned char, to ensure that the values are within the correct range. Casting a negative-valued char or signed char directly to int will produce a negative-valued int, which will be outside the range of allowed values (unless it happens to be equal to EOF, but even that would not give the desired result).