perror - Online Linux Manual PageSection : 3
Updated : 2023-02-05
Source : Linux man-pages 6.03

NAMEperror − print a system error message

LIBRARYStandard 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

DESCRIPTIONThe 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.

VERSIONSSince glibc 2.32, the declarations of sys_errlist and sys_nerr are no longer exposed by <stdio.h>.

ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7). InterfaceAttributeValue perror() Thread safetyMT-Safe race:stderr

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

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

SEE ALSOerr(3), errno(3), error(3), strerror(3)
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