The tolower() function has as a domain a type int, the
value of which is representable as an unsigned char
or the value of EOF. If the argument has any other value, the behavior
is undefined. If the argument of tolower() represents
an uppercase letter, and there exists a corresponding lowercase letter
(as defined by character type information in the program
locale category LC_CTYPE ), the result shall be the
corresponding lowercase letter. All other arguments in the domain
are returned unchanged.
Upon successful completion, tolower() shall return the lowercase
letter corresponding to the argument passed; otherwise,
it shall return the argument unchanged.
No errors are defined.
The following sections are informative.
setlocale() , the Base Definitions volume of IEEE Std 1003.1-2001,
Chapter 7, Locale, <ctype.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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