'\" t .\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk) .\" and Copyright (C) 2005, 2014, 2020 Michael Kerrisk .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .\" References consulted: .\" Linux libc source code .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) .\" 386BSD man pages .\" Modified Sat Jul 24 18:05:30 1993 by Rik Faith .\" Modified Fri Feb 16 14:25:17 1996 by Andries Brouwer .\" Modified Sun Jul 21 20:55:44 1996 by Andries Brouwer .\" Modified Mon Oct 15 21:16:25 2001 by John Levon .\" Modified Tue Oct 16 00:04:43 2001 by Andries Brouwer .\" Modified Fri Jun 20 03:04:30 2003 by Andries Brouwer .\" 2005-12-13, mtk, Substantial rewrite of strerror_r() description .\" Addition of extra material on portability and standards. .\" .TH strerror 3 2023-10-31 "Linux man-pages 6.06" .SH NAME strerror, strerrorname_np, strerrordesc_np, strerror_r, strerror_l \- return string describing error number .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B #include .P .BI "char *strerror(int " errnum ); .BI "const char *strerrorname_np(int " errnum ); .BI "const char *strerrordesc_np(int " errnum ); .P .BI "int strerror_r(int " errnum ", char " buf [. buflen "], size_t " buflen ); /* XSI-compliant */ .P .BI "char *strerror_r(int " errnum ", char " buf [. buflen "], size_t " buflen ); /* GNU-specific */ .P .BI "char *strerror_l(int " errnum ", locale_t " locale ); .fi .P .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .P .BR strerrorname_np (), .BR strerrordesc_np (): .nf _GNU_SOURCE .fi .P .BR strerror_r (): .nf The XSI-compliant version is provided if: (_POSIX_C_SOURCE >= 200112L) && ! _GNU_SOURCE Otherwise, the GNU-specific version is provided. .fi .SH DESCRIPTION The .BR strerror () function returns a pointer to a string that describes the error code passed in the argument .IR errnum , possibly using the .B LC_MESSAGES part of the current locale to select the appropriate language. (For example, if .I errnum is .BR EINVAL , the returned description will be "Invalid argument".) This string must not be modified by the application, and the returned pointer will be invalidated on a subsequent call to .BR strerror () or .BR strerror_l (), or if the thread that obtained the string exits. No other library function, including .BR perror (3), will modify this string. .P Like .BR strerror (), the .BR strerrordesc_np () function returns a pointer to a string that describes the error code passed in the argument .IR errnum , with the difference that the returned string is not translated according to the current locale. .P The .BR strerrorname_np () function returns a pointer to a string containing the name of the error code passed in the argument .IR errnum . For example, given .B EPERM as an argument, this function returns a pointer to the string "EPERM". Given .B 0 as an argument, this function returns a pointer to the string "0". .\" .SS strerror_r() .BR strerror_r () is like .BR strerror (), but might use the supplied buffer .I buf instead of allocating one internally. This function is available in two versions: an XSI-compliant version specified in POSIX.1-2001 (available since glibc 2.3.4, but not POSIX-compliant until glibc 2.13), and a GNU-specific version (available since glibc 2.0). The XSI-compliant version is provided with the feature test macros settings shown in the SYNOPSIS; otherwise the GNU-specific version is provided. If no feature test macros are explicitly defined, then (since glibc 2.4) .B _POSIX_C_SOURCE is defined by default with the value 200112L, so that the XSI-compliant version of .BR strerror_r () is provided by default. .P The XSI-compliant .BR strerror_r () is preferred for portable applications. It returns the error string in the user-supplied buffer .I buf of length .IR buflen . .P The GNU-specific .BR strerror_r () returns a pointer to a string containing the error message. This may be either a pointer to a string that the function stores in .IR buf , or a pointer to some (immutable) static string (in which case .I buf is unused). If the function stores a string in .IR buf , then at most .I buflen bytes are stored (the string may be truncated if .I buflen is too small and .I errnum is unknown). The string always includes a terminating null byte (\[aq]\e0\[aq]). .\" .SS strerror_l() .BR strerror_l () is like .BR strerror (), but maps .I errnum to a locale-dependent error message in the locale specified by .IR locale . The behavior of .BR strerror_l () is undefined if .I locale is the special locale object .B LC_GLOBAL_LOCALE or is not a valid locale object handle. .SH RETURN VALUE The .BR strerror (), .BR strerror_l (), and the GNU-specific .BR strerror_r () functions return the appropriate error description string, or an "Unknown error nnn" message if the error number is unknown. .P On success, .BR strerrorname_np () and .BR strerrordesc_np () return the appropriate error description string. If .I errnum is an invalid error number, these functions return NULL. .P The XSI-compliant .BR strerror_r () function returns 0 on success. On error, a (positive) error number is returned (since glibc 2.13), or \-1 is returned and .I errno is set to indicate the error (before glibc 2.13). .P POSIX.1-2001 and POSIX.1-2008 require that a successful call to .BR strerror () or .BR strerror_l () shall leave .I errno unchanged, and note that, since no function return value is reserved to indicate an error, an application that wishes to check for errors should initialize .I errno to zero before the call, and then check .I errno after the call. .SH ERRORS .TP .B EINVAL The value of .I errnum is not a valid error number. .TP .B ERANGE Insufficient storage was supplied to contain the error description string. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lb lb lbx l l l. Interface Attribute Value T{ .na .nh .BR strerror () T} Thread safety T{ .na .nh MT-Safe T} T{ .na .nh .BR strerrorname_np (), .BR strerrordesc_np () T} Thread safety MT-Safe T{ .na .nh .BR strerror_r (), .BR strerror_l () T} Thread safety MT-Safe .TE .P Before glibc 2.32, .BR strerror () is not MT-Safe. .SH STANDARDS .TP .BR strerror () C11, POSIX.1-2008. .TP .BR strerror_r () .\" FIXME . for later review when Issue 8 is one day released... .\" A future POSIX.1 may remove strerror_r() .\" http://austingroupbugs.net/tag_view_page.php?tag_id=8 .\" http://austingroupbugs.net/view.php?id=508 .TQ .BR strerror_l () POSIX.1-2008. .TP .BR strerrorname_np () .TQ .BR strerrordesc_np () GNU. .P POSIX.1-2001 permits .BR strerror () to set .I errno if the call encounters an error, but does not specify what value should be returned as the function result in the event of an error. On some systems, .\" e.g., Solaris 8, HP-UX 11 .BR strerror () returns NULL if the error number is unknown. On other systems, .\" e.g., FreeBSD 5.4, Tru64 5.1B .BR strerror () returns a string something like "Error nnn occurred" and sets .I errno to .B EINVAL if the error number is unknown. C99 and POSIX.1-2008 require the return value to be non-NULL. .SH HISTORY .TP .BR strerror () POSIX.1-2001, C89. .TP .BR strerror_r () POSIX.1-2001. .TP .BR strerror_l () glibc 2.6. POSIX.1-2008. .TP .BR strerrorname_np () .TQ .BR strerrordesc_np () glibc 2.32. .SH NOTES .BR strerrorname_np () and .BR strerrordesc_np () are thread-safe and async-signal-safe. .SH SEE ALSO .BR err (3), .BR errno (3), .BR error (3), .BR perror (3), .BR strsignal (3), .BR locale (7), .BR signal-safety (7)