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PERROR(3) Library Functions Manual PERROR(3)

write error messages to standard error

#include <stdio.h>

perror(const char *string);

The perror() function looks up the error message string affiliated with an error number and writes it, followed by a new-line, to the standard error stream.

If the argument string is not the NULL pointer and is not zero length, it is prepended to the message string and separated from it by a colon and a space (‘’). Otherwise, only the error message string is printed.

The contents of the error message string are the same as those returned by strerror() with argument errno.

intro(2), psignal(3), setlocale(3), strerror(3)

The perror() function conforms to ANSI X3.159-1989 (“ANSI C89”).

The perror() function first appeared in Version 4 AT&T UNIX.

On systems other than OpenBSD, the LC_MESSAGES locale(1) category can cause different strings to be printed instead of the normal error messages; see CAVEATS in setlocale(3) for details.
May 16, 2019 OpenBSD-current