Doubt in Structure padding with Pointer data types

[vickywiz]

code below gives O/P 4 when sizeof(obj) is computed..how it works..is structure padding different for pointer data types..

#include <stdio.h>
struct x
{
double *a;
};
int main()
{
struct x obj;
printf("%d\n",sizeof(obj));
return 0;
}

[leppyr64]

I'm not certain what you mean by structure padding. I would expect 4 to be the output.