perror(3) — Linux manual page

perror(3)               Library Functions Manual               perror(3)

NAME

       perror - print a system error message

LIBRARY

       Standard 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

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.

ATTRIBUTES

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌─────────────────────────┬───────────────┬─────────────────────┐
       │ Interface               │ Attribute     │ Value               │
       ├─────────────────────────┼───────────────┼─────────────────────┤
       │ perror()                │ Thread safety │ MT-Safe race:stderr │
       └─────────────────────────┴───────────────┴─────────────────────┘

STANDARDS

       errno
       perror()
              C11, POSIX.1-2008.

       sys_nerr
       sys_errlist
              BSD.

HISTORY

       errno
       perror()
              POSIX.1-2001, C89, 4.3BSD.

       sys_nerr
       sys_errlist
              Removed in glibc 2.32.

SEE ALSO

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

COLOPHON

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Linux man-pages 6.9.1          2024-06-15                      perror(3)

Pages that refer to this page: err(3), errno(3), error(3), fmtmsg(3), pmerrstr(3), psignal(3), sd_journal_print(3), stdio(3), strerror(3)

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