perror(3) man page

PERROR(3)              FreeBSD Library Functions Manual              PERROR(3)

NAME
       perror, errno - system error messages

SYNOPSIS
       void perror(s)
       char *s;

       #include <errno.h>

       int sys_nerr;
       char *sys_errlist[];
       int errno;

DESCRIPTION
       perror() produces a short error message on the standard error
       describing the last error encountered during a call to a system or
       library function.  If s is not a NULL pointer and does not point to a
       null string, the string it points to is printed, followed by a colon,
       followed by a space, followed by the message and a NEWLINE.  If s is a
       NULL pointer or points to a null string, just the message is printed,
       followed by a NEWLINE.  To be of most use, the argument string should
       include the name of the program that incurred the error.  The error
       number is taken from the external variable errno (see intro(2)), which
       is set when errors occur but not cleared when non-erroneous calls are
       made.

       To simplify variant formatting of messages, the vector of message
       strings sys_errlist is provided; errno can be used as an index in this
       table to get the message string without the newline.  sys_nerr is the
       number of messages provided for in the table; it should be checked
       because new error codes may be added to the system before they are
       added to the table.

SEE ALSO
       intro(2), psignal(3)

                                6 December 1988                      PERROR(3)

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