NAME¶
perror - print a system error message
SYNOPSIS¶
#include <stdio.h>
void perror(const char *s);
#include <errno.h>
const char *sys_errlist[];
int sys_nerr;
DESCRIPTION¶
The routine
perror() produces a message on the standard error output,
describing the last error encountered during a call to a system or library
function. The argument string
s is printed first, then a colon and a
blank, then the message and a new-line. To be of most use, the argument string
should include the name of the function that incurred the error. The error
number is taken from the external variable
errno, which is set when
errors occur but not cleared when non-erroneous calls are made.
The global error list
sys_errlist[] indexed by
errno can be used
to obtain the error message without the newline. The largest message number
provided in the table is
sys_nerr -1. Be careful when directly
accessing this list because new error values may not have been added to
sys_errlist[].
When a system call fails, it usually returns -1 and sets the variable
errno to a value describing what went wrong. (These values can be found
in
<errno.h>.) Many library functions do likewise. The function
perror() serves to translate this error code into human-readable form.
Note that
errno is undefined after a successful library call: this call
may well change this variable, even though it succeeds, for example because it
internally used some other library function that failed. Thus, if a failing
call is not immediately followed by a call to
perror, the value of
errno should be saved.
ANSI C, BSD 4.3, POSIX, X/OPEN
SEE ALSO¶
strerror(3)