NAME
errno — XSI error
return value
SYNOPSIS
#include <errno.h>
DESCRIPTION
errno is used by many XSI 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 will 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. The value of errno should
only be examined when it is indicated to be valid by a function's return
value. Programs should obtain the definition of
errno by the inclusion of
<errno.h>. The practice of defining
errno in a program as
extern
int errno is obsolescent. No function in
this specification sets errno to 0 to indicate an
error.
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
behaviour is undefined.
The symbolic values stored in errno are
documented in the ERRORS sections on all relevant pages.
RETURN VALUE
None.
ERRORS
None.
EXAMPLES
None.
APPLICATION USAGE
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 .
A program that uses errno for error
checking should set it to 0 before a function call, then inspect it before a
subsequent function call.
FUTURE DIRECTIONS
None.
SEE ALSO
<errno.h> , errors .
DERIVATION
Derived from Issue 1 of the SVID.