C - Find the size of structure

Question

I was asked this as interview question. Couldn\'t answer.

Write a C program to find size of structure without using the sizeof operator.

Answer 1

For people that like C macro style coding, here is my take on this:

#define SIZE_OF_STRUCT(mystruct)     \
   ({ struct nested_##mystruct {     \
         struct mystruct s;          \
         char end[0];                \
      } __attribute__((packed)) var; \
      var.end - (char *)&var; })

void main()
{
   struct mystruct {
      int c;
   };

   printf("size %d\n", SIZE_OF_STRUCT(mystruct));
}