NAME

ctype: isdigit, isxdigit, islower, isupper, isalpha, isalnum, isspace, iscntrl, ispunct, isprint, isgraph, isascii − character handling

SYNOPSIS

#include <ctype.h>
int isalpha(int c);
int isupper(int c);
int islower(int c);
int isdigit(int c);
int isxdigit(int c);
int isalnum(int c);
int isspace(int c);
int ispunct(int c);
int isprint(int c);
int isgraph(int c);
int iscntrl(int c);
int isascii(int c);

DESCRIPTION

These macros classify character-coded integer values.  Each is a predicate returning non-zero for true, zero for false.  The behavior of these macros, except isascii, is affected by the current locale [see setlocale(3C)].  To modify the behavior, change the LC_TYPE category in setlocale, that is, setlocale (LC_CTYPE, newlocale).  In the C locale, or in a locale where character type information is not defined, characters are classified according to the rules of the US-ASCII 7-bit coded character set. 

The macro isascii is defined on all integer values; the rest are defined only where the argument is an int, the value of which is representable as an unsigned char, or EOF, which is defined by the stdio.h header file and represents end-of-file. 

isalpha tests for any character for which isupper or islower is true, or any character that is one of an implementation-defined set of characters for which none of iscntrl, isdigit, ispunct, or isspace is true.  In the C locale, isalpha returns true only for the characters for which isupper or islower is true. 

isupper tests for any character that is an upper-case letter or is one of an implementation-defined set of characters for which none of iscntrl, isdigit, ispunct, isspace, or islower is true.  In the C locale, isupper returns true only for the characters defined as upper-case ASCII characters. 

islower tests for any character that is a lower-case letter or is one of an implementation-defined set of characters for which none of iscntrl, isdigit, ispunct, isspace, or isupper is true.  In the C locale, islower returns true only for the characters defined as lower-case ASCII characters. 

isdigit tests for any decimal-digit character. 

isxdigit tests for any hexadecimal-digit character ([0−9], [A−F] or [a−f]). 

isalnum tests for any character for which isalpha or isdigit is true (letter or digit). 

isspace tests for any space, tab, carriage-return, newline, vertical-tab or form-feed (standard white-space characters) or for one of an implementation-defined set of characters for which isalnum is false.  In the C locale, isspace returns true only for the standard white-space characters. 

ispunct tests for any printing character which is neither a space nor a character for which isalnum is true. 

isprint tests for any printing character, including space (" "). 

isgraph tests for any printing character, except space. 

iscntrl tests for any “control character” as defined by the character set. 

isascii tests for any ASCII character, code between 0 and 0177 inclusive. 

All the character classification macros and the conversion functions and macros use a table lookup. 

Functions exist for all the above defined macros.  To get the function form, the macro name must be undefined (for example, #undef isdigit). 

FILES

/usr/lib/locale/locale/LC_CTYPE

SEE ALSO

chrtbl(1M), setlocale(3C), stdio(3S), ascii(5), environ(5)

DIAGNOSTICS

If the argument to any of the character handling macros is not in the domain of the function, the result is undefined. 

  —  C Programming Language Utilities