A const member or a reference member cannot be initialized within an object’s constructor. Instead, they must be initialized in the constructor’s member-initializer list. Conceptually, mem-initialization takes place before the constructor, so by the time it is invoked, all const and reference members have already been assigned a value:

 class mem {	int &ri;  const int k; //both must be mem-initialized 	mem(int i, int j) : ri(i), k(j) {} };

Similarly, when a constructor in a derived class has to pass arguments to its base class constructor, a mem-initializer must be used:

 class base {	int num1;	char * text;	//no default constructor, arguments must be supplied	base(int n1, char * t) {num1 = n1; text = t; }};class derived : public base {	char *buf	derived (int n, char * t) : base(n, t) { buf = new char[100];}};