1STRERROR(3)                Linux Programmer's Manual               STRERROR(3)
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NAME

6       strerror,  strerror_r, strerror_l - return string describing error num‐
7       ber
8

SYNOPSIS

10       #include <string.h>
11
12       char *strerror(int errnum);
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14       int strerror_r(int errnum, char *buf, size_t buflen);
15                   /* XSI-compliant */
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17       char *strerror_r(int errnum, char *buf, size_t buflen);
18                   /* GNU-specific */
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20       char *strerror_l(int errnum, locale_t locale);
21
22   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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24       strerror_r():
25           The XSI-compliant version is provided if:
26           (_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE
27           Otherwise, the GNU-specific version is provided.
28

DESCRIPTION

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

70       The  strerror(),  strerror_l(), and the GNU-specific strerror_r() func‐
71       tions return the appropriate error description string, or  an  "Unknown
72       error nnn" message if the error number is unknown.
73
74       The  XSI-compliant  strerror_r()  function  returns  0  on success.  On
75       error, a (positive) error number is returned (since glibc 2.13), or  -1
76       is  returned  and  errno  is  set to indicate the error (glibc versions
77       before 2.13).
78
79       POSIX.1-2001 and POSIX.1-2008 require that a successful  call  to  str‐
80       error()  or  strerror_l()  shall  leave errno unchanged, and note that,
81       since no function return value is reserved to  indicate  an  error,  an
82       application  that wishes to check for errors should initialize errno to
83       zero before the call, and then check errno after the call.
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ERRORS

86       EINVAL The value of errnum is not a valid error number.
87
88       ERANGE Insufficient storage was supplied to contain the error  descrip‐
89              tion string.
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VERSIONS

92       The strerror_l() function first appeared in glibc 2.6.
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ATTRIBUTES

95       For   an   explanation   of   the  terms  used  in  this  section,  see
96       attributes(7).
97
98       ┌───────────────┬───────────────┬─────────────────────────┐
99Interface      Attribute     Value                   
100       ├───────────────┼───────────────┼─────────────────────────┤
101strerror()     │ Thread safety │ MT-Unsafe race:strerror │
102       ├───────────────┼───────────────┼─────────────────────────┤
103strerror_r(),  │ Thread safety │ MT-Safe                 │
104strerror_l()   │               │                         │
105       └───────────────┴───────────────┴─────────────────────────┘

CONFORMING TO

107       strerror() is specified by POSIX.1-2001, POSIX.1-2008,  C89,  and  C99.
108       strerror_r() is specified by POSIX.1-2001 and POSIX.1-2008.
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110       strerror_l() is specified in POSIX.1-2008.
111
112       The GNU-specific strerror_r() function is a nonstandard extension.
113
114       POSIX.1-2001  permits strerror() to set errno if the call encounters an
115       error, but does not specify what value should be returned as the  func‐
116       tion  result  in  the  event  of an error.  On some systems, strerror()
117       returns NULL if the error number is unknown.  On  other  systems,  str‐
118       error()  returns  a string something like "Error nnn occurred" and sets
119       errno to EINVAL if the error number is unknown.  C99  and  POSIX.1-2008
120       require the return value to be non-NULL.
121

NOTES

123       The  GNU  C  Library  uses  a buffer of 1024 characters for strerror().
124       This buffer size therefore should be  sufficient  to  avoid  an  ERANGE
125       error when calling strerror_r() and strerror_l().
126

SEE ALSO

128       err(3), errno(3), error(3), perror(3), strsignal(3), locale(7)
129

COLOPHON

131       This  page  is  part of release 4.16 of the Linux man-pages project.  A
132       description of the project, information about reporting bugs,  and  the
133       latest     version     of     this    page,    can    be    found    at
134       https://www.kernel.org/doc/man-pages/.
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138                                  2017-09-15                       STRERROR(3)
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