c++ - ポインターで変換コンストラクターを使用するにはどうすればよいですか？

Answer 1

Conversion constructors can only be defined for user defined types, in your case A. However, they do not apply to fundamental types as pointers like A*.

If doSomething was taking an A const& instead (or simply an A), then the conversion constructor would be invoked as you expect.

Answer 2

If you main requirement is to be able to call the existing doSomething function, then you can do this:

int main()
{
    C* object = new C();
    A a(object);
    doSomething(&a);
    // May need to delete object here -- depends on ownership semantics.
}

Answer 3

おそらく、CをAのサブクラスにしたいということです。

class C : public A {
...
};