1ERRNO(P)                   POSIX Programmer's Manual                  ERRNO(P)
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NAME

6       errno - error return value
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SYNOPSIS

9       #include <errno.h>
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DESCRIPTION

12       The lvalue errno is used by many functions to return error values.
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14       Many functions provide an error number in errno, which has type int and
15       is defined in <errno.h>. The value of errno shall be defined only after
16       a  call  to  a function for which it is explicitly stated to be set and
17       until it is changed by the next function call  or  if  the  application
18       assigns  it a value. The value of errno should only be examined when it
19       is indicated to be valid by a function's  return  value.   Applications
20       shall  obtain the definition of errno by the inclusion of <errno.h>. No
21       function in this volume of IEEE Std 1003.1-2001 shall set errno to 0.
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23       It is unspecified whether errno is a macro or  an  identifier  declared
24       with  external linkage. If a macro definition is suppressed in order to
25       access an actual object, or a program defines an  identifier  with  the
26       name errno, the behavior is undefined.
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28       The  symbolic  values stored in errno are documented in the ERRORS sec‐
29       tions on all relevant pages.
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RETURN VALUE

32       None.
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ERRORS

35       None.
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37       The following sections are informative.
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EXAMPLES

40       None.
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APPLICATION USAGE

43       Previously both POSIX and X/Open documents were more  restrictive  than
44       the  ISO C  standard  in  that  they required errno to be defined as an
45       external variable, whereas the ISO C standard required only that  errno
46       be defined as a modifiable lvalue with type int.
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48       An  application  that  needs to examine the value of errno to determine
49       the error should set it to 0 before a function call,  then  inspect  it
50       before a subsequent function call.
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RATIONALE

53       None.
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FUTURE DIRECTIONS

56       None.
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SEE ALSO

59       Error  Numbers  ,  the Base Definitions volume of IEEE Std 1003.1-2001,
60       <errno.h>
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63       Portions of this text are reprinted and reproduced in  electronic  form
64       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
65       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
66       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
67       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
68       event of any discrepancy between this version and the original IEEE and
69       The Open Group Standard, the original IEEE and The Open Group  Standard
70       is  the  referee document. The original Standard can be obtained online
71       at http://www.opengroup.org/unix/online.html .
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75IEEE/The Open Group                  2003                             ERRNO(P)
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