1STRERROR(3) Linux Programmer's Manual STRERROR(3)
2
6 strerror, strerrorname_np, strerrordesc_np, strerror_r, strerror_l -
7 return string describing error number
8
10 #include <string.h>
11 char *strerror(int errnum);
13 const char *strerrorname_np(int errnum);
14 const char *strerrordesc_np(int errnum);
15 int strerror_r(int errnum, char *buf, size_t buflen);
17 /* XSI-compliant */
18 char *strerror_r(int errnum, char *buf, size_t buflen);
20 /* GNU-specific */
21 char *strerror_l(int errnum, locale_t locale);
23 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
25 strerrorname_np(), strerrordesc_np():
27 _GNU_SOURCE
28 strerror_r():
29 The XSI-compliant version is provided if:
30 (_POSIX_C_SOURCE >= 200112L) && ! _GNU_SOURCE
31 Otherwise, the GNU-specific version is provided.
32
34 The strerror() function returns a pointer to a string that describes
35 the error code passed in the argument errnum, possibly using the
36 LC_MESSAGES part of the current locale to select the appropriate lan‐
37 guage. (For example, if errnum is EINVAL, the returned description
38 will be "Invalid argument".) This string must not be modified by the
39 application, but may be modified by a subsequent call to strerror() or
40 strerror_l(). No other library function, including perror(3), will
41 modify this string.
42 Like strerror(), the strerrordesc_np() function returns a pointer to a
44 string that describes the error code passed in the argument errnum,
45 with the difference that the returned string is not translated accord‐
46 ing to the current locale.
47 The strerrorname_np() function returns a pointer to a string containing
49 the name of the error code passed in the argument errnum. For example,
50 given EPERM as an argument, this function returns a pointer to the
51 string "EPERM".
52 strerror_r()
54 The strerror_r() function is similar to strerror(), but is thread safe.
55 This function is available in two versions: an XSI-compliant version
56 specified in POSIX.1-2001 (available since glibc 2.3.4, but not POSIX-
57 compliant until glibc 2.13), and a GNU-specific version (available
58 since glibc 2.0). The XSI-compliant version is provided with the fea‐
59 ture test macros settings shown in the SYNOPSIS; otherwise the GNU-spe‐
60 cific version is provided. If no feature test macros are explicitly
61 defined, then (since glibc 2.4) _POSIX_C_SOURCE is defined by default
62 with the value 200112L, so that the XSI-compliant version of str‐
63 error_r() is provided by default.
64 The XSI-compliant strerror_r() is preferred for portable applications.
66 It returns the error string in the user-supplied buffer buf of length
67 buflen.
68 The GNU-specific strerror_r() returns a pointer to a string containing
70 the error message. This may be either a pointer to a string that the
71 function stores in buf, or a pointer to some (immutable) static string
72 (in which case buf is unused). If the function stores a string in buf,
73 then at most buflen bytes are stored (the string may be truncated if
74 buflen is too small and errnum is unknown). The string always includes
75 a terminating null byte ('\0').
76 strerror_l()
78 strerror_l() is like strerror(), but maps errnum to a locale-dependent
79 error message in the locale specified by locale. The behavior of str‐
80 error_l() is undefined if locale is the special locale object
81 LC_GLOBAL_LOCALE or is not a valid locale object handle.
82
84 The strerror(), strerror_l(), and the GNU-specific strerror_r() func‐
85 tions return the appropriate error description string, or an "Unknown
86 error nnn" message if the error number is unknown.
87 On success, strerrorname_np() and strerrordesc_np() return the appro‐
89 priate error description string. If errnum is an invalid error number,
90 these functions return NULL.
91 The XSI-compliant strerror_r() function returns 0 on success. On er‐
93 ror, a (positive) error number is returned (since glibc 2.13), or -1 is
94 returned and errno is set to indicate the error (glibc versions before
95 2.13).
96 POSIX.1-2001 and POSIX.1-2008 require that a successful call to str‐
98 error() or strerror_l() shall leave errno unchanged, and note that,
99 since no function return value is reserved to indicate an error, an ap‐
100 plication that wishes to check for errors should initialize errno to
101 zero before the call, and then check errno after the call.
102
104 EINVAL The value of errnum is not a valid error number.
105 ERANGE Insufficient storage was supplied to contain the error descrip‐
107 tion string.
108
110 The strerror_l() function first appeared in glibc 2.6.
111
113 For an explanation of the terms used in this section, see at‐
114 tributes(7).
115 ┌───────────────────┬───────────────┬─────────────────────────┐
117 │Interface │ Attribute │ Value │
118 ├───────────────────┼───────────────┼─────────────────────────┤
119 │strerror() │ Thread safety │ MT-Unsafe race:strerror │
120 ├───────────────────┼───────────────┼─────────────────────────┤
121 │strerrorname_np(), │ Thread safety │ MT-Safe │
122 │strerrordesc_np() │ │ │
123 ├───────────────────┼───────────────┼─────────────────────────┤
124 │strerror_r(), │ Thread safety │ MT-Safe │
125 │strerror_l() │ │ │
126 └───────────────────┴───────────────┴─────────────────────────┘
128 strerror() is specified by POSIX.1-2001, POSIX.1-2008, C89, and C99.
129 strerror_r() is specified by POSIX.1-2001 and POSIX.1-2008.
130 strerror_l() is specified in POSIX.1-2008.
132 The GNU-specific functions strerror_r(), strerrorname_np(), and str‐
134 errordesc_np() are nonstandard extensions.
135 POSIX.1-2001 permits strerror() to set errno if the call encounters an
137 error, but does not specify what value should be returned as the func‐
138 tion result in the event of an error. On some systems, strerror() re‐
139 turns NULL if the error number is unknown. On other systems, str‐
140 error() returns a string something like "Error nnn occurred" and sets
141 errno to EINVAL if the error number is unknown. C99 and POSIX.1-2008
142 require the return value to be non-NULL.
143
145 The GNU C Library uses a buffer of 1024 characters for strerror().
146 This buffer size therefore should be sufficient to avoid an ERANGE er‐
147 ror when calling strerror_r().
148 strerrorname_np() and strerrordesc_np() are thread-safe and async-sig‐
150 nal-safe.
151
153 err(3), errno(3), error(3), perror(3), strsignal(3), locale(7)
154
156 This page is part of release 5.10 of the Linux man-pages project. A
157 description of the project, information about reporting bugs, and the
158 latest version of this page, can be found at
159 https://www.kernel.org/doc/man-pages/.
160 2020-11-01 STRERROR(3)