April 17, 2008 CTYPE 3

### NAME

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

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```int` `c`
isalpha(```c`) isupper(```c`) islower(```c`) isdigit(```c`) isxdigit(```c`) isalnum(```c`) isspace(```c`) ispunct(```c`) isprint(```c`) isgraph(```c`) iscntrl(```c`) isblank(```c`) toupper(```c`) tolower(```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 on stdout, use the following code: `

    const char *s = ...;
    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 ANSI X3.159-1989 (``ANSI C89'') .

### CAVEATS

The first argument of these functions is of type 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 Passing invalid values leads to undefined behavior.

Values of type 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 or must first be cast to to ensure that the values are within the correct range. The result should then be cast to to avoid warnings from some compilers. Casting a negative-valued or directly to will produce a negative-valued 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).