Man page - sys_errlist(3)

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Manual

perror

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
ATTRIBUTES
STANDARDS
HISTORY
SEE ALSO

NAME

perror - print a system error message

LIBRARY

Standard C library ( libc , -lc )

SYNOPSIS

#include <stdio.h>

void perror(const char * s );

#include <errno.h>

int errno ; /* Not really declared this way; see errno(3) */

[[deprecated]] const char *const sys_errlist [];
[[deprecated]] int sys_nerr ;

Feature Test Macro Requirements for glibc (see feature_test_macros (7)):

sys_errlist , sys_nerr :
From glibc 2.19 to glibc 2.31:
_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).

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STANDARDS

errno

perror ()

C11, POSIX.1-2008.

sys_nerr
sys_errlist

BSD.

HISTORY

errno

perror ()

POSIX.1-2001, C89, 4.3BSD.

sys_nerr
sys_errlist

Removed in glibc 2.32.

SEE ALSO

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