problem with sizeof operator

Question

As i want to find array size dynamically in function, i used sizeof operator. But i got some unexpected result. here is one demo program to show you, what i want to do.

Answer 1

To prevent this type of accidental misuse of sizeof, you can define a function which only works on arrays:

template
int array_size(T (&)[N]) {
  return N;
}

If you use this in your code, you'll see a compiler error when applied to S1, as it is not an array. Plus, it's shorter and a bit more explicit than sizeof array / sizeof array[0] (using the size of the first item means you don't have to repeat the array type).

This also already exists in Boost in a more general form (accepting anything with a size method, such as std::vector).