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ERRNO(3P)                  POSIX Programmer's Manual                 ERRNO(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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  sec-
       tions 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(3P)