CTYPE(3) BSD Library Functions Manual CTYPE(3)NAME
isalpha, isupper, islower, isdigit, isxdigit, isalnum, isspace, ispunct,
isprint, isgraph, iscntrl, isblank, toupper, tolower, — character classi‐
fication and mapping functions
LIBRARY
Standard C Library (libc, -lc)
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 inte‐
ger c.
See the specific manual pages for information about the test or conver‐
sion 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 ALSOisalnum(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. The result
should then be cast to int to avoid warnings from some compilers. Cast‐
ing 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).
BSD May 6, 2010 BSD
