Template function that returns default constructed value

Question

I have a function that returns default constructed value of template type:

template<typename T>
T do_stuff()
{
    return T();
}

I use it like this:

int main(int argc, char** argv)
{
    std::string str("hello");
    int a = 10;
    int *p = &a;

    str = do_stuff<std::string>();
    a = do_stuff<int>();
    p = do_stuff<int*>();

    return 0;
}

After I use it I have: str is an empty string, a eqauls 0 and p is a null pointer. I can understand why std::string variable becomes an empty string (it has default constructor that constructs an empty string). But why an int variable becomes 0 and a pointer becomes a null pointer. Is it default template behaviour?

I use gcc 4.6.6 under Linux Centos.

Answer 1

From this reference on value initialization:

• If T is a class type with at least one user-provided constructor of any kind, the default constructor is called.

• If T is an non-union class type without any user-provided constructors, then the object is zero-initialized and then the implicitly-declared default constructor is called (unless it's trivial)

• If T is an array type, each element of the array is value-initialized

• Otherwise, the object is zero-initialized.

What is happening is that the last point in the above list.