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Linux 2.6 - man page for errno (linux section 3posix)

ERRNO(P)			    POSIX Programmer's Manual				 ERRNO(P)

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 defini-
       tion  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 link-
       age. 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 stan-
       dard 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					 ERRNO(P)


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