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

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

       errno - error return value

       #include <errno.h>

       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 defi-
       nition  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  defini-
       tion 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.



       The following sections are informative.


       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.



       Error Numbers, the Base Definitions volume of IEEE Std 1003.1-2001, <errno.h>

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at .

IEEE/The Open Group                  2003                            ERRNO(3P)