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 correspond-
       ing 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 applica-
       tion 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.   Appli-
       cations	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 Technol-
       ogy -- 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)