Question

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What is this weird colon-member syntax in the constructor?

I’m trying to understand what this kind of code means

Say I have this

class OptionStudent: public Student // derived class from Student class
{
    public:
        explicit OptionStudent(const std::string id = "12345678", 
                               const std::string first = "someone")
        : Student(id, first)
        {
             count_++;
        }
}

What is that colon after the “someone”): <– part called or mean for this constructor?
I know the constructor may be a little incorrect but I don’t know what this is called. I just copied my notes from what the instructor was writing on the board and didn’t understand it.
Something to do with the class or object remembering something?

Answer 1

It is the member initialization list. In this case, it calls the base class’s constructor with id and first as arguments. It could also provide initial values for non-static data members of your class (if you had any).

Note that the semicolon after Student(id, first); is a syntax error and needs to be removed.