_tolower man page


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.

_tolower — transliterate uppercase characters to lowercase


#include <ctype.h>

int _tolower(int c);


The _tolower() macro shall be equivalent to tolower(c) except that the application shall ensure that the argument c is an uppercase letter.

Return Value

Upon successful completion, _tolower() shall return the lowercase letter corresponding to the argument passed.


No errors are defined.

The following sections are informative.

Application Usage

Applications should use the tolower() function instead of the obsolescent _tolower() function.

Future Directions

The _tolower() function may be removed in a future version.

See Also

tolower(), isupper()

The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale, <ctype.h>


2013 IEEE/The Open Group POSIX Programmer's Manual