For strerror(): 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
IEEE Std 1003.1-2001 defers to the ISO C standard.
The strerror() function shall map the error number in errnum to a
locale-dependent error message string and shall return a pointer to it.
Typically, the values for errnum come from errno, but
strerror() shall map any value of type int to a message.
The string pointed to shall not be modified by the application, but may be
overwritten by a subsequent call to strerror() or
The contents of the error message strings returned by strerror() should
be determined by the setting of the LC_MESSAGES category in the current
The implementation shall behave as if no function defined in this volume of
IEEE Std 1003.1-2001 calls strerror().
The strerror() function shall not change the setting of errno if
Since no return value is reserved to indicate an error, an application wishing
to check for error situations should set errno to 0, then call
strerror(), then check errno.
The strerror() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
The strerror_r() function shall map the error number in errnum to
a locale-dependent error message string and shall return the string in the
buffer pointed to by strerrbuf, with length buflen.
Upon successful completion, strerror() shall return a pointer to the
generated message string. On error errno may be set, but no return
value is reserved to indicate an error.
Upon successful completion, strerror_r() shall return 0. Otherwise, an
error number shall be returned to indicate the error.
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 http://www.opengroup.org/unix/online.html