Predict the output of following C++ program.
A's constructor A's constructor A's Assignment Operator B's constructor
The first line of output is printed by the statement “A a1;” in main().
The second line is printed when B’s member ‘a’ is initialized. This is important.
The third line is printed by the statement “this->a = a;” in B’s constructor.
The fourth line is printed by cout statement in B’s constructor.
If we take a closer look at the above code, the constructor of class B is not efficient as member ‘a’ is first constructed with default constructor, and then the values from the parameter are copied using assignment operator. It may be a concern when class A is big, which generally is the case with many practical classes. See the following optimized code.
A's constructor A's Copy constructor B's constructor
The constructor of class B now uses initializer list to initialize its member ‘a’. When Initializer list is used, the member ‘a’ of class B is initialized directly from the parameter. So a call to A’s constructor is reduced.
In general, it is a good idea to use Initializer List to initialize all members of a class, because it saves one extra assignment of members. See point 6 of this post for more details.
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