| .\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" and Copyright (C) 2005, 2014, 2020 Michael Kerrisk <mtk.manpages@gmail.com> |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
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| .\" preserved on all copies. |
| .\" |
| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
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| .\" which is licensed free of charge, as they might when working |
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| .\" Formatted or processed versions of this manual, if unaccompanied by |
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| .\" %%%LICENSE_END |
| .\" |
| .\" 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 <faith@cs.unc.edu> |
| .\" Modified Fri Feb 16 14:25:17 1996 by Andries Brouwer <aeb@cwi.nl> |
| .\" Modified Sun Jul 21 20:55:44 1996 by Andries Brouwer <aeb@cwi.nl> |
| .\" Modified Mon Oct 15 21:16:25 2001 by John Levon <moz@compsoc.man.ac.uk> |
| .\" Modified Tue Oct 16 00:04:43 2001 by Andries Brouwer <aeb@cwi.nl> |
| .\" Modified Fri Jun 20 03:04:30 2003 by Andries Brouwer <aeb@cwi.nl> |
| .\" 2005-12-13, mtk, Substantial rewrite of strerror_r() description |
| .\" Addition of extra material on portability and standards. |
| .\" |
| .TH STRERROR 3 2021-03-22 "" "Linux Programmer's Manual" |
| .SH NAME |
| strerror, strerrorname_np, strerrordesc_np, strerror_r, strerror_l \- return string describing error number |
| .SH SYNOPSIS |
| .nf |
| .B #include <string.h> |
| .PP |
| .BI "char *strerror(int " errnum ); |
| .BI "const char *strerrorname_np(int " errnum ); |
| .BI "const char *strerrordesc_np(int " errnum ); |
| .PP |
| .BI "int strerror_r(int " errnum ", char *" buf ", size_t " buflen ); |
| /* XSI-compliant */ |
| .PP |
| .BI "char *strerror_r(int " errnum ", char *" buf ", size_t " buflen ); |
| /* GNU-specific */ |
| .PP |
| .BI "char *strerror_l(int " errnum ", locale_t " locale ); |
| .fi |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR strerrorname_np (), |
| .BR strerrordesc_np (): |
| .nf |
| _GNU_SOURCE |
| .fi |
| .PP |
| .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, but may be |
| modified by a subsequent call to |
| .BR strerror () |
| or |
| .BR strerror_l (). |
| No other library function, including |
| .BR perror (3), |
| will modify this string. |
| .PP |
| 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. |
| .PP |
| 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 |
| .BR EPERM |
| as an argument, this function returns a pointer to the string "EPERM". |
| .\" |
| .SS strerror_r() |
| The |
| .BR strerror_r () |
| function is similar to |
| .BR strerror (), |
| but is |
| thread safe. |
| 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. |
| .PP |
| 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 . |
| .PP |
| 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 |
| .BR 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. |
| .PP |
| 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. |
| .PP |
| 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 (glibc versions before 2.13). |
| .PP |
| 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 VERSIONS |
| The |
| .BR strerror_l () |
| function first appeared in glibc 2.6. |
| .PP |
| The |
| .BR strerrorname_np () |
| and |
| .BR strerrordesc_np () |
| functions first appeared in glibc 2.32. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lb lb lbx |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR strerror () |
| T} Thread safety T{ |
| MT-Unsafe race:strerror |
| T} |
| T{ |
| .BR strerrorname_np (), |
| .BR strerrordesc_np () |
| T} Thread safety MT-Safe |
| T{ |
| .BR strerror_r (), |
| .BR strerror_l () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| .BR strerror () |
| is specified by POSIX.1-2001, POSIX.1-2008, C89, and C99. |
| .BR strerror_r () |
| is specified by POSIX.1-2001 and POSIX.1-2008. |
| .\" 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 |
| .PP |
| .BR strerror_l () |
| is specified in POSIX.1-2008. |
| .PP |
| The GNU-specific functions |
| .BR strerror_r (), |
| .BR strerrorname_np (), |
| and |
| .BR strerrordesc_np () |
| are nonstandard extensions. |
| .PP |
| 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 NOTES |
| The GNU C Library uses a buffer of 1024 characters for |
| .BR strerror (). |
| This buffer size therefore should be sufficient to avoid an |
| .B ERANGE |
| error when calling |
| .BR strerror_r (). |
| .PP |
| .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) |