NAME

       errno - error return value

SYNOPSIS

       #include <errno.h>

DESCRIPTION

       The lvalue errno is used by many functions to return error values.

       Many  functions  provide  an  error  number in errno, which has type int and is defined in <errno.h>. The
       value of errno shall be defined only after a call to a function for which it is explicitly stated  to  be
       set and until it is changed by the next function call or if the application assigns it a value. The value
       of  errno  should  only  be  examined  when  it  is  indicated  to be valid by a function's return value.
       Applications shall obtain the definition of errno by the inclusion of  <errno.h>.  No  function  in  this
       volume of IEEE Std 1003.1-2001 shall set errno to 0.

       It  is  unspecified  whether errno is a macro or an identifier declared with external linkage. If a macro
       definition is suppressed in order to access an actual object, or a program defines an identifier with the
       name errno, the behavior is undefined.

       The symbolic values stored in errno are documented in the ERRORS sections on all relevant pages.

RETURN VALUE

       None.

ERRORS

       None.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Previously both POSIX and X/Open documents were more restrictive than the ISO C  standard  in  that  they
       required errno to be defined as an external variable, whereas the ISO C standard required only that errno
       be defined as a modifiable lvalue with type int.

       An  application that needs to examine the value of errno to determine the error should set it to 0 before
       a function call, then inspect it before a subsequent function call.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Error Numbers , the Base Definitions volume of IEEE Std 1003.1-2001, <errno.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                              ERRNO(P)