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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>


       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 .