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PERROR(3) Linux Programmer's Manual PERROR(3) 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: From glibc 2.19 to 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 correspondβ ing 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 proβ vided 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. 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). ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ¬ββββββββββββββββ¬ββββββββββββββββββββββ βInterface β Attribute β Value β ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββΌββββββββββββββββΌββββββββββββββββββββββ€ βperror() β Thread safety β MT-Safe race:stderr β ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββββββββ 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 err(3), errno(3), error(3), strerror(3) 2021-03-22 PERROR(3)