CODEWITHSUNDEEP
c++classc++11constructormember
Bojan
Bojan

Reputation: 69

Can class member be initialized with another class member in the initializer list?

Suppose I have class with two members,

class App
{
public:
   App() : window(1366, 768, "Title"), drawer(window) {}
private:
   Window window;
   Drawer drawer;
}

and the Drawer class has constructor Drawer(const Window&).
Is it valid to initialize the App class member Drawer with the another class member Window, like in this example?

Upvotes: 2

Views: 85

Answers (2)

P.W
P.W

Reputation: 26800

The non-static data members are initialized in order of declaration in the class definition. So in this particular instance it works as window is declared before drawer in the definition of App. But if you change the order, this will not work as intended.

But a compiler will warn you about this with appropriate warning level. GCC 8.2 with -Wall option issues the following warnings if the order is reversed.

#1 with x86-64 gcc 8.2
<source>: In constructor 'App::App()':

<source>:16:14: warning: 'App::window' will be initialized after [-Wreorder]
       Window window;
              ^~~~~~

<source>:15:14: warning:   'Drawer App::drawer' [-Wreorder]
       Drawer drawer;
              ^~~~~~

<source>:13:4: warning:   when initialized here [-Wreorder]
    App() : window(1366, 768), drawer(window) {}
    ^~~

As drawer is initialized first, it will not be initialized with the window object that has been constructed with the values 1366 and 768.

Upvotes: 1

Jarod42
Jarod42

Reputation: 217275

Yes, following is valid:

class App
{
public:
   App() : window(1366, 768, "Title"), drawer(window) {}
private:
   Window window;
   Drawer drawer;
};

Upvotes: 2

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