perror, errno - print system error messages
#include <stdio.h> void perror(const char *s)
The perror() function produces a message on the standard error output (file descriptor 2) describing the last error encountered by the thread during a call to a system or library function. The argument string s is printed, followed by a colon and a blank, followed by the message and a NEWLINE character. If s is a null pointer or points to a null string, the colon is not printed. The argument string should include the name of the program that incurred the error. The error number is taken from the errno macro defined in <errno.h>. This per-thread value is set when errors occur but not cleared when non-erroneous calls are made. See Intro(2).
Messages printed from this function are in the native language specified by the LC_MESSAGES locale category. See setlocale(3C).
See attributes(7) for descriptions of the following attributes: