strerror(3)

NAME

   strerror,  strerror_r,  strerror_l  -  return  string  describing error
   number

SYNOPSIS

   #include <string.h>

   char *strerror(int errnum);

   int strerror_r(int errnum, char *buf, size_t buflen);
               /* XSI-compliant */

   char *strerror_r(int errnum, char *buf, size_t buflen);
               /* GNU-specific */

   char *strerror_l(int errnum, locale_t locale);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   strerror_r():
       The XSI-compliant version is provided if:
       (_POSIX_C_SOURCE >= 200112L) && !  _GNU_SOURCE
       Otherwise, the GNU-specific version is provided.

DESCRIPTION

   The strerror() function returns a pointer to a  string  that  describes
   the  error  code  passed  in  the  argument  errnum, possibly using the
   LC_MESSAGES part of  the  current  locale  to  select  the  appropriate
   language.   (For example, if errnum is 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 strerror() or
   strerror_l().  No other library  function,  including  perror(3),  will
   modify this string.

   strerror_r()
   The strerror_r() function is similar to 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) _POSIX_C_SOURCE is defined  by  default
   with   the   value  200112L,  so  that  the  XSI-compliant  version  of
   strerror_r() is provided by default.

   The XSI-compliant strerror_r() is preferred for portable  applications.
   It  returns  the error string in the user-supplied buffer buf of length
   buflen.

   The GNU-specific 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 buf, or a pointer to some (immutable) static  string
   (in which case buf is unused).  If the function stores a string in buf,
   then at most buflen bytes are stored (the string may  be  truncated  if
   buflen is too small and errnum is unknown).  The string always includes
   a terminating null byte ('\0').

   strerror_l()
   strerror_l() is like strerror(), but maps errnum to a  locale-dependent
   error  message  in  the  locale  specified  by locale.  The behavior of
   strerror_l() is undefined  if  locale  is  the  special  locale  object
   LC_GLOBAL_LOCALE or is not a valid locale object handle.

RETURN VALUE

   The   strerror(),   strerror_l(),  and  the  GNU-specific  strerror_r()
   functions return  the  appropriate  error  description  string,  or  an
   "Unknown error nnn" message if the error number is unknown.

   The  XSI-compliant  strerror_r()  function  returns  0  on success.  On
   error, a (positive) error number is returned (since glibc 2.13), or  -1
   is  returned  and  errno  is  set to indicate the error (glibc versions
   before 2.13).

   POSIX.1-2001  and  POSIX.1-2008  require  that  a  successful  call  to
   strerror()  or strerror_l() shall leave 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 errno to
   zero before the call, and then check errno after the call.

ERRORS

   EINVAL The value of errnum is not a valid error number.

   ERANGE Insufficient  storage  was  supplied  to   contain   the   error
          description string.

VERSIONS

   The strerror_l() function first appeared in glibc 2.6.

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   
   Interface       Attribute      Value                   
   
   strerror()      Thread safety  MT-Unsafe race:strerror 
   
   strerror_r(),   Thread safety  MT-Safe                 
   strerror_l()                                           
   

CONFORMING TO

   strerror() is specified by POSIX.1-2001, POSIX.1-2008,  C89,  and  C99.
   strerror_r() is specified by POSIX.1-2001 and POSIX.1-2008.

   strerror_l() is specified in POSIX.1-2008.

   The GNU-specific strerror_r() function is a nonstandard extension.

   POSIX.1-2001  permits strerror() to set 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, strerror()
   returns NULL if  the  error  number  is  unknown.   On  other  systems,
   strerror()  returns  a  string  something like "Error nnn occurred" and
   sets errno  to  EINVAL  if  the  error  number  is  unknown.   C99  and
   POSIX.1-2008 require the return value to be non-NULL.

SEE ALSO

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

COLOPHON

   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at
   https://www.kernel.org/doc/man-pages/.

                              2016-10-08                       STRERROR(3)

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