Simple use of va_list

# Include <stdarg. h>

# Define _ INTSIZEOF (n) (sizeof (n) + sizeof (int)-1 )&~ (Sizeof (int)-1 ))
# Define va_start (ap, v) (ap = (va_list) & v + _ INTSIZEOF (v) // The first optional parameter address
# Define va_arg (ap, t) (* (t *) (ap + = _ INTSIZEOF (t)-_ INTSIZEOF (t) // The next parameter address
# Define va_end (ap) (ap = (va_list) 0) // set the pointer to invalid

Sample Code
Void arg_test (int I ,...);
Int main (int argc, char * argv [])
{
Int int_size = _ INTSIZEOF (int );
Printf ("int_size = % d \ n", int_size );
Arg_test (0, 4 );

Arg_cnt (4, 1, 2, 3, 4 );
Return 0;
}
Void arg_test (int I ,...)
{
Int j = 0;
Va_list arg_ptr;

Va_start (arg_ptr, I );
Printf ("& I = % p \ n", & I); // print the address of parameter I in the stack
Printf ("arg_ptr = % p \ n", arg_ptr );
// Print the arg_ptr address after va_start,
// It should be higher than the address of parameter I in sizeof (int) bytes
// Arg_ptr points to the address of the next parameter.

J = * (int *) arg_ptr );
Printf ("% d \ n", I, j );
J = va_arg (arg_ptr, int );
Printf ("arg_ptr = % p \ n", arg_ptr );
// Print the address of arg_ptr after va_arg
// It should be higher than the sizeof (int) byte before calling va_arg
// Arg_ptr points to the address of the next parameter.
Va_end (arg_ptr );
Printf ("% d \ n", I, j );
}