Why must const members be initialized in the constructor initializer rather than in its body?

c++ constructor initialization constants
Namratha Patil picture Namratha Patil · Dec 10, 2008 · Viewed 32.6k times · Source

Why must class members declared as const be initialized in the constructor initializer list rather than in the constructor body?

What is the difference between the two?

Answer

Vladimir picture Vladimir · Dec 10, 2008

In C++, an object is considered fully initialised when execution enters the body of the constructor.

You said:

"i wanted to know why const must be intialized in constructor initializer list rather than in it's body ?."

What you are missing is that initialisation happens in the initialisation list, and assignment happens in the body of the constructor. The steps in logic:

1) A const object can only be initialised.

2) An object has all of its members initialised in the initialisation list. Even if you do not explicitly initialise them there, the compiler will happily do so for you :-)

3) Therefore, putting 1) and 2) together, a member which is const can only ever have a value assigned to it at initialisation, which happens during the initialisation list.

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