perror

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 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.

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).

       ┌──────────┬───────────────┬─────────────────────┐
       │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 5.09 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/.



                                   2020-11-01                          PERROR(3)