perror

<html> <head> <title>perror</title> <META NAME="KEYWORDS" CONTENT="perror"> </head> <body BGCOLOR="#ffffff" LINK="#0000ff" VLINK="#0000ff" ALINK="#0000ff" TEXT="#000000"> <center> <h1>perror</h1></center> <PRE> <A HREF="/man3/PERROR">PERROR(3)</A> Linux Programmer's Manual <A HREF="/man3/PERROR">PERROR(3)</A> 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 <A HREF="/man3/errno">errno(3)</A> */ Feature Test Macro Requirements for glibc (see <A HREF="/man7/feature_test_macros">feature_test_macros(7)</A>): 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 func- tion. 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 dep- recated; use <A HREF="/man3/strerror">strerror(3)</A> 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 fol- lowed by a call to perror(), the value of errno should be saved. ATTRIBUTES For an explanation of the terms used in this section, see at- <A HREF="/man7/tributes">tributes(7)</A>. +----------+---------------+---------------------+ |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 <A HREF="/man3/err">err(3)</A>, <A HREF="/man3/errno">errno(3)</A>, <A HREF="/man3/error">error(3)</A>, <A HREF="/man3/strerror">strerror(3)</A> COLOPHON This page is part of release 5.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2019-03-06 <A HREF="/man3/PERROR">PERROR(3)</A></PRE> <center> <h6>Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2025 <a href="http://www.he.net">Hurricane Electric</a>. All Rights Reserved.</h6></center> </body> </html>

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