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perror

Section: C Library Functions (3)
Updated: 202-0-08
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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;  R]/* 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 ([aq][rs]0[aq])), 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 ne-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 huma-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	M-Safe race:stderr

STANDARDS

errno: perror() C11, POSIX.-2008.
sys_nerr: sys_errlist BSD.

HISTORY

errno: perror() POSIX.-2001, C89, 4.3BSD.
sys_nerr: sys_errlist Removed in glibc 2.32.