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NAME

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

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <string.h>

       char *strerror(int errnum);
       const char *strerrorname_np(int errnum);
       const char *strerrordesc_np(int errnum);

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

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

       char *strerror_l(int errnum, locale_t locale);

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

       strerrorname_np(), strerrordesc_np():
           _GNU_SOURCE

       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, and the returned  pointer  will  be  invalidated  on  a  subsequent  call  to
       strerror()  or  strerror_l(),  or  if the thread that obtained the string exits.  No other
       library function, including perror(3), will modify this string.

       Like strerror(), the strerrordesc_np()  function  returns  a  pointer  to  a  string  that
       describes  the  error  code  passed  in  the argument errnum, with the difference that the
       returned string is not translated according to the current locale.

       The strerrorname_np() function returns a pointer to a string containing the  name  of  the
       error  code  passed in the argument errnum.  For example, given EPERM as an argument, this
       function returns a pointer to the string "EPERM".  Given 0 as an argument,  this  function
       returns a pointer to the string "0".

   strerror_r()
       strerror_r()  is  like  strerror(),  but  might  use  the  supplied  buffer buf instead of
       allocating one internally.  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.

       On  success,  strerrorname_np()  and  strerrordesc_np()  return  the   appropriate   error
       description string.  If errnum is an invalid error number, these functions return NULL.

       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 (before glibc 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.

ATTRIBUTES

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

       ┌───────────────────┬───────────────┬─────────────────────────────────────────────────────┐
       │InterfaceAttributeValue                                               │
       ├───────────────────┼───────────────┼─────────────────────────────────────────────────────┤
       │strerror()         │ Thread safety │ MT-Safe                                             │
       ├───────────────────┼───────────────┼─────────────────────────────────────────────────────┤
       │strerrorname_np(), │ Thread safety │ MT-Safe                                             │
       │strerrordesc_np()  │               │                                                     │
       ├───────────────────┼───────────────┼─────────────────────────────────────────────────────┤
       │strerror_r(),      │ Thread safety │ MT-Safe                                             │
       │strerror_l()       │               │                                                     │
       └───────────────────┴───────────────┴─────────────────────────────────────────────────────┘
       Before glibc 2.32, strerror() is not MT-Safe.

STANDARDS

       strerror()
              C11, POSIX.1-2008.

       strerror_r()
       strerror_l()
              POSIX.1-2008.

       strerrorname_np()
       strerrordesc_np()
              GNU.

       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.

HISTORY

       strerror()
              POSIX.1-2001, C89.

       strerror_r()
              POSIX.1-2001.

       strerror_l()
              glibc 2.6.  POSIX.1-2008.

       strerrorname_np()
       strerrordesc_np()
              glibc 2.32.

NOTES

       strerrorname_np() and strerrordesc_np() are thread-safe and async-signal-safe.

SEE ALSO

       err(3), errno(3), error(3), perror(3), strsignal(3), locale(7), signal-safety(7)