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Tip of the Day
Language: C++
Expertise: All
Apr 16, 1998

Calling an object's member function from its constructor

An object's member functions (both virtual and non-virtual) can be called from its constructor. The invoked virtual is guaranteed to be the one defined in the current object (or higher, if it has not been overridden in the current object). However, virtuals of objects derived from the one whose constructor is being executed are not called.
 
class A {
	public:
	virtual void f() {}
	virtual void g() {}
};
class B: public  A {
	public:
	void f () {} //overriding A::f()
	B() { f(); //calls B::f()
		g(); //g() not overriden in B, therefore calling A::g()  }
};
Mind that if the object's member functions use object data members, it is the implementor's responsibility to initialize them first, preferably by a mem-initializer list:
 
class C {
	int n;
	int  getn() const { cout<<n<<endl; }
	public:
	C(int j) : n(j) { getn(); } //Fine: n initialized before getn() 
//is called; otherwise - n would
//have an undefined value };
Danny Kalev
 
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