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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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 differ (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 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.
None.
None.
The following sections are informative.
None.
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.
None.
None.
Section 2.3, Error Numbers
The Base Definitions volume of POSIX.1‐2008, errno.h(0p)
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 http://www.unix.org/online.html .
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 ERRNO(3P)
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