HP 3000 Manuals HP 3000 Manuals
va_arg
Initializes a variable to the beginning of an argument list.
Syntax
#include <stdarg.h>
type va_arg (va_list ap, type);
Parameters
ap A pointer to a double, as defined by type va_list in
<varargs.h>. This variable must be initialized with the
macro va_start.
type A data type, either built-in or user-defined.
Return Values
x The value of the next argument in the call,
returned as a variable of type type.
Description
This macro returns the value of the next argument in the argument list of
functions that can be called with a variable number of arguments.
The macros va_start, va_arg, and va_end determine the arguments of
functions with variable-length argument lists. Functions with
variable-length argument lists are indicated by the ellipsis in the
function header.
Successive invocations of va_arg return the values of the remaining
arguments in succession. The ap argument is used by the macro to
maintain the context of each successive call. This argument must be
initialized by a call to va_start prior to calling va_arg.
The macro assumes that the return value is of type type. No error
checking is performed. If there is no next argument when va_arg is
called , or if type is not compatible with the type of the actual next
argument, the value returned is unpredictable.
When writing functions with a variable number of arguments, you should
provide a method for the calling procedure to either pass the number of
actual arguments, or signal the end of the argument list. In addition,
the calling program and function being called must cooperate closely as
to the data types of the items in the variable argument list.
NOTE The header <varargs.h> also contains this macro. However,
<varargs.h> header is not defined by the ANSI C standard.
Examples
Refer to the example located in the va_start macro description.
See Also
va_start, va_end, ANSI C 4.8.1.2