c++constructorexplicitexplicit-constructor

explicit non-single parameter constructor

Can anyone explain why does non-single parameter constructor marked as explicit compile? As far as I understand this is absolutely useless keyword here, so why does this compile without error?

class X
{
public:
    explicit X(int a, int b) { /* ... */}
};
Solution

  • In C++03, and in this particular case, it makes no sense for a two parameter constructor to be marked explicit. But it could make sense here:

    explicit X(int i, int j=42);

    So, marking a two parameter constructor with explicit does not have to be an error.

    In C++11, this use of explicit would prevent you from doing this:

    X x = {1,2};