When object variable is reassigned in C++, what happens to the original object?

Question

When an object variable is reassigned in C++, what happens to the original value? In the code below an object is created onto the stack and placed in variable. Then a new object is created on the stack and placed in the same variable. What happens to the original object? Does it stay on the stack until variable goes out of scope?

void foo() {
    ClassName variable(a, b); // variable created on the stack
    variable = ClassName(c, d); // new value for variable created on stack
    ...
}

Answer 1

What happens is that the class's assignment operator is called. In most cases that just means that the contents of the old object are updated with values from the new object. So if ClassName is:

struct ClassName
{
    int a;
    int b;

    ClassName(int a, int b) : a(a), b(b) {}
};

In this case the default assignment operator would be called which would be equivalent to:

    ClassName& operator=(const ClassName& other)
    {
        a = other.a;
        b = other.b;
        return *this;
    }

For classes that have dynamic content there would be a bit more to do, but the results will generally be the same. Since the assignment operator can be overridden, anything could theoretically happen but this is what we expect.