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+'\" et
+.TH ERRNO "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.SH PROLOG
+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.
+
+.SH NAME
+errno
+\(em error return value
+.SH SYNOPSIS
+.LP
+.nf
+#include <errno.h>
+.fi
+.SH DESCRIPTION
+The lvalue
+.IR errno
+is used by many functions to return error values.
+.P
+Many functions provide an error number in
+.IR errno ,
+which has type
+.BR int
+and is defined in
+.IR <errno.h> .
+The value of
+.IR 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
+.IR errno
+should only be examined when it is indicated to be valid by a
+function's return value. Applications shall obtain the definition of
+.IR errno
+by the inclusion of
+.IR <errno.h> .
+No function in this volume of POSIX.1\(hy2008 shall set
+.IR errno
+to 0. The setting of
+.IR errno
+after a successful call to a function is unspecified unless the
+description of that function specifies that
+.IR errno
+shall not be modified.
+.P
+It is unspecified whether
+.IR 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
+.IR errno ,
+the behavior is undefined.
+.P
+The symbolic values stored in
+.IR errno
+are documented in the ERRORS sections on all relevant pages.
+.SH "RETURN VALUE"
+None.
+.SH ERRORS
+None.
+.LP
+.IR "The following sections are informative."
+.SH EXAMPLES
+None.
+.SH "APPLICATION USAGE"
+Previously both POSIX and X/Open documents were more restrictive than
+the ISO\ C standard in that they required
+.IR errno
+to be defined as an external variable, whereas the ISO\ C standard required only
+that
+.IR errno
+be defined as a modifiable lvalue with type
+.BR int .
+.P
+An application that needs to examine the value of
+.IR errno
+to determine the error should set it to 0 before a function call, then
+inspect it before a subsequent function call.
+.SH RATIONALE
+None.
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.IR "Section 2.3" ", " "Error Numbers"
+.P
+The Base Definitions volume of POSIX.1\(hy2008,
+.IR "\fB<errno.h>\fP"
+.SH COPYRIGHT
+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 .