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@c Documentation of gnulib module 'c-ctype'.

@c Copyright (C) 2008--2025 Free Software Foundation, Inc.

@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>.

@mindex c-ctype
The @code{c-ctype} module contains functions operating on single-byte
characters, like the functions in @code{<ctype.h>}, that operate as if the
locale encoding was ASCII@.  (The "C" locale on many systems has the locale
encoding "ASCII".)

The functions are:
@smallexample
extern bool c_isascii (int c);

extern bool c_isalnum (int c);
extern bool c_isalpha (int c);
extern bool c_isblank (int c);
extern bool c_iscntrl (int c);
extern bool c_isdigit (int c);
extern bool c_islower (int c);
extern bool c_isgraph (int c);
extern bool c_isprint (int c);
extern bool c_ispunct (int c);
extern bool c_isspace (int c);
extern bool c_isupper (int c);
extern bool c_isxdigit (int c);

extern int c_tolower (int c);
extern int c_toupper (int c);
@end smallexample

These functions assign properties only to ASCII characters.

The @var{c} argument can be a @code{char} or @code{unsigned char} value,
whereas the corresponding functions in @code{<ctype.h>} take an argument
that is actually an @code{unsigned char} value.

The @code{c_is*} functions return @samp{bool}, where the corresponding
functions in @code{<ctype.h>} return @samp{int} for historical reasons.

Note: The @code{<ctype.h>} functions support only unibyte locales.
kc3-lang/gnulib/doc/c-ctype.texi

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doc/c-ctype.texi
