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 .