When I ran the program below in the Linux system, I can't get the expected answer "9". But I can get it in the windows system.
Why does this happen?
#include <stdio.h>
int sum(int num, ...){
int* p = &num + 1;
int res = 0;
while(num--){
res += *p++;
}
return res;
}
int main(){
printf("%d\n", sum(3,2,3,4));
return 0;
}
I debug it in GDB, shown as below: enter image description here
My System configuration is below.
Linux version 5.11.0-41-generic (buildd@lgw01-amd64-005) (gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, GNU ld (GNU Binutils for Ubuntu) 2.34)
You need to use macros defined in the header <stdarg.h>.
Here you are.
#include <stdio.h>
#include <stdarg.h>
long long int sum( size_t n, ... )
{
long long int result = 0;
va_list ap;
va_start( ap, n );
while (n--)
{
result += va_arg( ap, int );
}
va_end( ap );
return result;
}
int main( void )
{
printf( "%lld\n", sum( 9, 1, 2, 3, 4, 5, 6, 7, 8, 9 ) );
}
The program output is
45