c语言函数的可选性自变量

 1 #include <stdio.h> 
 2 #include <stdarg.h> 
 3 int sum( int, ... );
 4 
 5     int main( void ) 
 6 {
 7 
 8     
 9 
10       int answer = sum( 4, 4, 3, 2, 1 );
11 
12       printf( "The answer is %d\n", answer );
13 
14     
15 
16       return( 0 );
17 
18 }
19 
20     
21 
22     int sum( int num, ... ) 
23 {
24 
25       int answer = 0;
26 
27       va_list argptr;
28 
29       va_start( argptr, num );
30 
31       for( ; num > 0; num-- )
32 
33         answer += va_arg( argptr, int );
34 
35       va_end( argptr );
36 
37       return( answer );
38 
39 }