strerror_r(3)

1strerror(3)                Library Functions Manual                strerror(3)
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NAME

6       strerror,  strerrorname_np,  strerrordesc_np,  strerror_r, strerror_l -
7       return string describing error number
8

LIBRARY

10       Standard C library (libc, -lc)
11

SYNOPSIS

13       #include <string.h>
14
15       char *strerror(int errnum);
16       const char *strerrorname_np(int errnum);
17       const char *strerrordesc_np(int errnum);
18
19       int strerror_r(int errnum, char buf[.buflen], size_t buflen);
20                      /* XSI-compliant */
21
22       char *strerror_r(int errnum, char buf[.buflen], size_t buflen);
23                      /* GNU-specific */
24
25       char *strerror_l(int errnum, locale_t locale);
26
27   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
28
29       strerrorname_np(), strerrordesc_np():
30           _GNU_SOURCE
31
32       strerror_r():
33           The XSI-compliant version is provided if:
34               (_POSIX_C_SOURCE >= 200112L) && ! _GNU_SOURCE
35           Otherwise, the GNU-specific version is provided.
36

DESCRIPTION

38       The strerror() function returns a pointer to a  string  that  describes
39       the  error  code  passed  in  the  argument  errnum, possibly using the
40       LC_MESSAGES part of the current locale to select the  appropriate  lan‐
41       guage.   (For  example,  if  errnum is EINVAL, the returned description
42       will be "Invalid argument".)  This string must not be modified  by  the
43       application,  but may be modified by a subsequent call to strerror() or
44       strerror_l().  No other library  function,  including  perror(3),  will
45       modify this string.
46
47       Like  strerror(), the strerrordesc_np() function returns a pointer to a
48       string that describes the error code passed  in  the  argument  errnum,
49       with  the difference that the returned string is not translated accord‐
50       ing to the current locale.
51
52       The strerrorname_np() function returns a pointer to a string containing
53       the name of the error code passed in the argument errnum.  For example,
54       given EPERM as an argument, this function  returns  a  pointer  to  the
55       string "EPERM".
56
57   strerror_r()
58       The strerror_r() function is similar to strerror(), but is thread safe.
59       This function is available in two versions:  an  XSI-compliant  version
60       specified  in POSIX.1-2001 (available since glibc 2.3.4, but not POSIX-
61       compliant until glibc 2.13),  and  a  GNU-specific  version  (available
62       since  glibc 2.0).  The XSI-compliant version is provided with the fea‐
63       ture test macros settings shown in the SYNOPSIS; otherwise the GNU-spe‐
64       cific  version  is  provided.  If no feature test macros are explicitly
65       defined, then (since glibc 2.4) _POSIX_C_SOURCE is defined  by  default
66       with  the  value  200112L,  so  that  the XSI-compliant version of str‐
67       error_r() is provided by default.
68
69       The XSI-compliant strerror_r() is preferred for portable  applications.
70       It  returns  the error string in the user-supplied buffer buf of length
71       buflen.
72
73       The GNU-specific strerror_r() returns a pointer to a string  containing
74       the  error  message.  This may be either a pointer to a string that the
75       function stores in buf, or a pointer to some (immutable) static  string
76       (in which case buf is unused).  If the function stores a string in buf,
77       then at most buflen bytes are stored (the string may  be  truncated  if
78       buflen is too small and errnum is unknown).  The string always includes
79       a terminating null byte ('\0').
80
81   strerror_l()
82       strerror_l() is like strerror(), but maps errnum to a  locale-dependent
83       error  message in the locale specified by locale.  The behavior of str‐
84       error_l()  is  undefined  if  locale  is  the  special  locale   object
85       LC_GLOBAL_LOCALE or is not a valid locale object handle.
86

RETURN VALUE

88       The  strerror(),  strerror_l(), and the GNU-specific strerror_r() func‐
89       tions return the appropriate error description string, or  an  "Unknown
90       error nnn" message if the error number is unknown.
91
92       On  success,  strerrorname_np() and strerrordesc_np() return the appro‐
93       priate error description string.  If errnum is an invalid error number,
94       these functions return NULL.
95
96       The  XSI-compliant  strerror_r() function returns 0 on success.  On er‐
97       ror, a (positive) error number is returned (since glibc 2.13), or -1 is
98       returned and errno is set to indicate the error (before glibc 2.13).
99
100       POSIX.1-2001  and  POSIX.1-2008  require that a successful call to str‐
101       error() or strerror_l() shall leave errno  unchanged,  and  note  that,
102       since no function return value is reserved to indicate an error, an ap‐
103       plication that wishes to check for errors should  initialize  errno  to
104       zero before the call, and then check errno after the call.
105

ERRORS

107       EINVAL The value of errnum is not a valid error number.
108
109       ERANGE Insufficient  storage was supplied to contain the error descrip‐
110              tion string.
111

ATTRIBUTES

113       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
114       tributes(7).
115
116       ┌───────────────────┬───────────────┬──────────────────────────────────┐
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       └───────────────────┴───────────────┴──────────────────────────────────┘
127

STANDARDS

129       strerror()
130              C11, POSIX.1-2008.
131
132       strerror_r()
133       strerror_l()
134              POSIX.1-2008.
135
136       strerrorname_np()
137       strerrordesc_np()
138              GNU.
139
140       POSIX.1-2001  permits strerror() to set errno if the call encounters an
141       error, but does not specify what value should be returned as the  func‐
142       tion  result in the event of an error.  On some systems, strerror() re‐
143       turns NULL if the error number is  unknown.   On  other  systems,  str‐
144       error()  returns  a string something like "Error nnn occurred" and sets
145       errno to EINVAL if the error number is unknown.  C99  and  POSIX.1-2008
146       require the return value to be non-NULL.
147

HISTORY

149       strerror()
150              POSIX.1-2001, C89.
151
152       strerror_r()
153              POSIX.1-2001.
154
155       strerror_l()
156              glibc 2.6.  POSIX.1-2008.
157
158       strerrorname_np()
159       strerrordesc_np()
160              glibc 2.32.
161

NOTES

163       The  GNU  C  Library  uses  a buffer of 1024 characters for strerror().
164       This buffer size therefore should be sufficient to avoid an ERANGE  er‐
165       ror when calling strerror_r().
166
167       strerrorname_np()  and strerrordesc_np() are thread-safe and async-sig‐
168       nal-safe.
169