perror - print a system error message
#include <stdio.h>
void perror(const char *s);
#include <errno.h>
const char *sys_errlist[];
int sys_nerr;
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 per-
ror() 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 per-
ror, the value of errno should be saved.
ANSI C, BSD 4.3, POSIX, X/OPEN
strerror(3)
1996-05-16 PERROR(3)
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