C++ : Is Member Initialization List Efficient ?

Yes it is, and should be made a habit. Consider the following example:

class Anjelina {

public:
// very naive ....
Anjelina( ) {
_name = 0; //_name is NULL now
_blemish = 0;
}

private:
String _name;
int _blemish;
};


What happens before the start of constructor call?

An object is fully constructed. What !!! Yes, it is. Before the constructor call, the 'this' pointer is initialized and all the members are constructed (their default constructors called). The member constructor is called if it is non-trivial. So, what's wrong in the above constructor? Nothing, it's just naive. The reason is, that the constructor of _name is already called and String already initialized to 0 (default behavior for String object). The code transformation that takes place is:

// Pseudo C++ Code
Angelina::Angelina (/* 'this' pointer goes here */) {
// invoke default String constructor
_name.String::String ( ) ;
// generate temporary
String temp = String ( 0 ) ;
// memberwise copy _name
_name.String::operator= ( temp ) ;
// destroy temporary
_name.String::~String( );

_blemish = 0 ;
}


So the proper code for constructor should be:

Anjelina( ):_name(0) {
_blemish = 0;
}

or even better (non-confusing code) ...

Anjelina( ):_name(0), _blemish(0) { }

This will call the constructor with 0 as an argument. If you want String's default constructor to be called, you can write _name( ).

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