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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>

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 .