Question

How to declare a constant array in class with constant class variable? Is it possible.
I don’t want dynamic array.

I mean something like this:

class test
{
    const int size;
    int array[size];
    public:
    test():size(50)
    {}
}

int main()
{
    test t(500);
    return 0;
}

the above code gives errors

Answer 1

No, it’s not possible: As long as size is a dynamic variable, array[size] cannot possibly be implemented as a static array.

If you like, think about it this way: sizeof(test) must be known at compile time (e.g. consider arrays of test). But sizeof(test) == sizeof(int) * (1 + size) in your hypothetical example, which isn’t a compile-time known value!

You can make size into a template parameter; that’s about the only solution:

template <unsigned int N>
class Test
{
  int array[N];
  static const unsigned int size = N; // unnecessary really
public:
  // ...
};

Usage: Test<50> x;

Note that now we have sizeof(Test<N>) == sizeof(int) * (1 + N), which is in fact a compile-time known value, because for each N, Test<N> is a distinct type.