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


       #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, 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)):

       strerrorname_np(), strerrordesc_np():

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


       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.

       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".

       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

       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.


       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 (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.


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

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


       The strerror_l() function first appeared in glibc 2.6.

       The strerrorname_np() and strerrordesc_np() functions first appeared in glibc 2.32.


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

       │InterfaceAttributeValue                                               │
       │strerror()         │ Thread safety │ MT-Unsafe race:strerror                             │
       │strerrorname_np(), │ Thread safety │ MT-Safe                                             │
       │strerrordesc_np()  │               │                                                     │
       │strerror_r(),      │ Thread safety │ MT-Safe                                             │
       │strerror_l()       │               │                                                     │


       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  functions  strerror_r(),  strerrorname_np(),  and strerrordesc_np() are
       nonstandard extensions.

       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-


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

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


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


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       found at

                                            2021-03-22                                STRERROR(3)