sys_nerr (3)

NAME

perror - print a system error message

SYNOPSIS

#include <stdio.h>
void perror(const char *s);
 
#include <errno.h>
const char * const sys_errlist[];
 
int sys_nerr;
 
int errno; /* Not really declared this way; see errno(3) */

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sys_errlist, sys_nerr:
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_BSD_SOURCE

DESCRIPTION

The perror() function produces a message on standard error describing the last error encountered during a call to a system or library function.
First (if s is not NULL and *s is not a null byte ('\0')), the argument string s is printed, followed by a colon and a blank. Then an error message corresponding to the current value of errno and a new-line.
To be of most use, the argument string should include the name of the function that incurred the error.
The global error list sys_errlist[], which can be 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[]. The use of sys_errlist[] is nowadays deprecated; use strerror(3) instead.
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 system call or library function 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.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
perror () Thread safety MT-Safe race:stderr
 

CONFORMING TO

perror(), errno: POSIX.1-2001, POSIX.1-2008, C89, C99, 4.3BSD.
The externals sys_nerr and sys_errlist derive from BSD, but are not specified in POSIX.1.

NOTES

The externals sys_nerr and sys_errlist are defined by glibc, but in <stdio.h>.

SEE ALSO

err(3), errno(3), error(3), strerror(3)

Information

Source
Linux kernel
OS/version
Source updated
September 15, 2017
Page created
February 9, 2018
Page generated
December 2, 2018