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[C++] Member initialization

General and Gameplay Programming Programming

Started by jrdmellow December 15, 2011 06:51 PM

4 comments, last by jrdmellow 12 years, 4 months ago

jrdmellow

125

Author

December 15, 2011 06:51 PM

A (hopefully) quick question;

Does this type of initialization have a name?



class MyClass

{

public:



    MyClass();

// ...

private:

    int m_count;

};



MyClass::MyClass()

    : m_count(0)    // <-- this guy right here

{

}

Are there any benefits/fallbacks to doing it this way as opposed to this;



MyClass::MyClass()

{

    m_count = 0;

}

Thanks!

PS - sorry if this has been posted before, it's hard to find something when you don't know it's name!

ApochPiQ

23,138

December 15, 2011 07:00 PM

Initialization lists.

Wielder of the Sacred Wands
[Work - ArenaNet] [Epoch Language] [Scribblings]

WavyVirus

885

December 15, 2011 07:05 PM

That is called an "initialization list".

Generally you should prefer using this method to assigning values in the body of the constructor. If you do it in the constructor body, the variable actually has its default constructor called before the constructor body is entered i.e. it is default-constructed and then immediately overwritten in the body of the constructor, which is wasteful (an extra constructor call).

There isn't actually a performance hit when using an int or similar built-in type, but it is still advisable to use the initialization list for the sake of consistency.

NightCreature83

5,061

December 15, 2011 07:05 PM

A (hopefully) quick question;

Does this type of initialization have a name?
class MyClass { public: MyClass(); // ... private: int m_count; }; MyClass::MyClass() : m_count(0) // <-- this guy right here { }

Are there any benefits/fallbacks to doing it this way as opposed to this;
MyClass::MyClass() { m_count = 0; }

Thanks!

PS - sorry if this has been posted before, it's hard to find something when you don't know it's name!