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:
	   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 ('')), 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 immedi-
       ately 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 | 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

       err(3), errno(3), error(3), strerror(3)

COLOPHON

       This  page is part of release 4.15 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/.

								    2017-09-15								 PERROR(3)