Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- test for an alphabetic character
int isalpha(int c);
int isalpha_l(int c, locale_t locale);
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here and the
ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.
functions shall test whether
is a character of class
in the current locale,
or in the locale represented by
respectively; see the Base Definitions volume of POSIX.1-2017,
Chapter 7, Locale.
argument is an
the value of which the application shall ensure is representable as an
or equal to the value of the macro EOF. If the argument has any other
value, the behavior is undefined.
The behavior is undefined if the
is the special locale object LC_GLOBAL_LOCALE or is not a valid locale
functions shall return non-zero if
is an alphabetic character; otherwise, they shall return 0.
No errors are defined.
The following sections are informative.
To ensure applications portability, especially across natural
languages, only these functions and the functions in the reference pages
listed in the SEE ALSO section should be used for character classification.
The Base Definitions volume of POSIX.1-2017,
Chapter 7, Locale,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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