sys_nerr (3) - Linux Manuals
sys_nerr: print a system error message
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:
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.
The externals
sys_nerr
and
sys_errlist
derive from BSD, but are not specified in POSIX.1.
DESCRIPTION
The
perror()
function produces a message on standard error describing the last
error encountered during a call to a system or library function.
VERSIONS
Since glibc version 2.32, the declarations of
sys_errlist
and
sys_nerr
are no longer exposed by
<stdio.h>.
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.
NOTES
The externals
sys_nerr
and
sys_errlist
are defined by glibc, but in
<stdio.h>.
COLOPHON
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man-pages
project.
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and the latest version of this page,
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https://www.kernel.org/doc/man-pages/.