int tolower(int c);
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.
COPYRIGHTPortions 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 http://www.opengroup.org/unix/online.html .