Re: constructor pain

From:

John Harrison <john_andronicus@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 10 Mar 2007 10:52:59 GMT

Message-ID:

<f6wIh.57171$z54.25148@newsfe3-gui.ntli.net>

Michael wrote:

Hi All,

why does this:

class Base {
    protected:
        int var;
    public:
        Base():var(0){};
        virtual int getVar() = 0;
};

class Class1 : public Base{
    protected:
        int otherVar;
    public:
    Class1():otherVar(1){};
    Class1(int i = 0):otherVar(i){};
        int getOtherVar(){return otherVar;}
        int getVar(){return var;}
};

give me an error:
error: call of overloaded `Class1()' is ambiguous
note: candidates are: Class1::Class1(int)
note: Class1::Class1()

I only have a single constructor that takes an int as a parameter, and a
default that takes no argument. Where is the ambiguity?

Because your constructor with an int as a parameter also has a default
value. So when you supply no arguments to your constructor either one
could be called. Seems very straightforward to me.

Ask yourself, if you write

Class1 c;

what did you expect the value of c.otherVar to be? If you expected it to
be 0, then remove your first constructor; if you expected it to be 1,
then remove the default argument from your second constructor.

john