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Simple constructor question (C++)

Started by Red Ant Jun 29, 2004 at 7:33 AM 4 replies 700+ views

Original Post

Jun 29, 2004 at 7:33 AM


class A
{
private:
    void init();
public:
    A();
    A( const A& rSource );
....
};

void A::init()
{
    // do stuff
}

A::A()
{
    init();
}

A::A( const A& rSource ) : A()
{
    // copy rSource or whatever
}

Is this: A::A( const A& rSource ) : A() legal? Meaning, will this invoke the default c'tor (and thus properly initialize the object) before doing the actual copy c'tor stuff? Haven't got a compiler here, so I can't try it out right now. :P Regards, Red Ant

Agony

178

Agony

Jun 29, 2004 at 7:41 AM

I don't think it works. Constructor calls in the initializer list must be either base class constructors, or member object constructors. At least, that's what I've always thought, and that's what MSVC6 enforces. Would be kinda nice if it were allowed, though. Might be a bit inefficient at times, but still convenient.

DrPizza

Jun 29, 2004 at 7:43 AM

Sadly not.

Red Ant

Author

Red Ant

Jun 29, 2004 at 8:45 AM

Oh ... too bad. Ah well, thanks anyway!

TangentZ

Jun 29, 2004 at 9:04 AM

Quote:
Original post by Red Ant
Is this: A::A( const A& rSource ) : A() legal? Meaning, will this invoke the default c'tor (and thus properly initialize the object) before doing the actual copy c'tor stuff?

That is not legal.

What you could do, though, is something like this.

class A    {    private:        X x;    public:        A() : x() { }        A(const A &other) : x(other.x) { }        // A(const A &other) { x = other.x; }  // Inefficient!    };// end

If X is costly to construct, you would want this anyway (invoke
the copy-constructor of X).

You wouldn't want to construct X and then copy X.

Red Ant

Author

Red Ant

Jun 29, 2004 at 9:28 AM

Good point, TangentZ, but then I usually write my copy methods more like:

x.copy( other.x ) rather than x = other.x; anyway. If that makes sense. :)

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