PERROR(3)                 Linux Programmer's Manual                PERROR(3)

NAME         top

       perror - print a system error message

SYNOPSIS         top

       #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: _BSD_SOURCE

DESCRIPTION         top

       The routine perror() produces a message on the standard error output,
       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 the message and a new-line.

       To be of most use, the argument string should include the name of the
       function that incurred the error.  The error number is taken from the
       external variable errno, which is set when errors occur but not
       cleared when successful calls are made.

       The global error list sys_errlist[] 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.

       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
       library 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         top

       For an explanation of the terms used in this section, see

       │Interface Attribute     Value               │
       │perror()  │ Thread safety │ MT-Safe race:stderr │

CONFORMING TO         top

       The function perror() and the external errno (see errno(3)) conform
       to C89, C99, 4.3BSD, POSIX.1-2001.  The externals sys_nerr and
       sys_errlist conform to BSD.

NOTES         top

       The externals sys_nerr and sys_errlist are defined by glibc, but in

SEE ALSO         top

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

COLOPHON         top

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                                 2015-04-19                        PERROR(3)