perror(3) - Linux manual page (original) (raw)

perror(3) Library Functions Manual perror(3)

NAME top

   perror - print a system error message

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <stdio.h>**

   **void perror(const char ***_s_**);**

   **#include <errno.h>**

   **int** _[errno](../man3/errno.3.html)_**;** /* Not really declared this way; see errno(3) */

   **[[deprecated]] const char *const** _syserrlist_**[];**
   **[[deprecated]] int** _sysnerr_**;**

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   _syserrlist_, _sysnerr_:
       From glibc 2.19 to glibc 2.31:
           _DEFAULT_SOURCE
       glibc 2.19 and earlier:
           _BSD_SOURCE

DESCRIPTION top

   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](../man3/errno.3.html)_
   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 _syserrlist_[], which can be indexed by
   _[errno](../man3/errno.3.html)_, can be used to obtain the error message without the
   newline.  The largest message number provided in the table is
   _sysnerr_-1.  Be careful when directly accessing this list, because
   new error values may not have been added to _syserrlist_[].  The
   use of _syserrlist_[] is nowadays deprecated; use [strerror(3)](../man3/strerror.3.html)
   instead.

   When a system call fails, it usually returns -1 and sets the
   variable _[errno](../man3/errno.3.html)_ 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](../man3/errno.3.html)_ 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](../man3/errno.3.html)_ should be saved.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────┬───────────────┬─────────────────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────┼───────────────┼─────────────────────┤
   │ **perror**()                 │ Thread safety │ MT-Safe race:stderr │
   └──────────────────────────┴───────────────┴─────────────────────┘

STANDARDS top

   _[errno](../man3/errno.3.html)_
   **perror**()
          C11, POSIX.1-2008.

   _sysnerr_
   _syserrlist_
          BSD.

HISTORY top

   _[errno](../man3/errno.3.html)_
   **perror**()
          POSIX.1-2001, C89, 4.3BSD.

   _sysnerr_
   _syserrlist_
          Removed in glibc 2.32.

SEE ALSO top

   [err(3)](../man3/err.3.html), [errno(3)](../man3/errno.3.html), [error(3)](../man3/error.3.html), [strerror(3)](../man3/strerror.3.html)

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Linux man-pages 6.10 2024-07-23 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)