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

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

       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 definition of errno by the inclusion of <errno.h>.  No
       function in this volume of POSIX.1-2008 shall set errno to 0. The
       setting of errno after a successful call to a function is unspecified
       unless the description of that function specifies that errno shall not
       be modified.

       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.



       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.



       Section 2.3, Error Numbers

       The Base Definitions volume of POSIX.1-2008, <errno.h>

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see .

IEEE/The Open Group                  2013                             ERRNO(3)