CTYPE(3)

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

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);

DESCRIPTION
The above functions perform character tests and conversions on the integer c.

See the specific manual pages for information about the test or conversion performed by each function.

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((int)(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 ansiC. All described functions, including isblank(), also conform to p1003.1-2001.

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. The result should then be cast to int to avoid warnings from some compilers. 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).