Question

Possible Duplicate:
declaring a const instance of a class
Why does C++ require a user-provided default constructor to default-construct a const object?

My program like this:

class c
{
};

int main()
{
    const c a;

    return 0;
}

when I compile it using g++, it prompt:

main.cpp:10:7: note: ‘const class c’ has no user-provided default constructor

Why, this is just an empty class and do not do anything, why I have to provide a user-provided constructor.

Answer 1

Because the language rules say so.

The constant must have its value set in the definition, as it cannot be assigned a value later. If you don’t explicitly provide a value, the type must have a default constructor.