Why must initializer list order match member declaration order?

Question

Why does gcc throw a hissy fit if the initializer list order doesn\'t match variable order in the class?

class myClass
{
public:
   int A;
   int B;
   myCla         


        

Answer 1

The warning is trying to prevent situations where you might be relying on the wrong ordering of the data members. Say you think B is initialized before A, and then you do something like this:

myClass::myClass() :
B(42), A(B) {}

Here, you have undefined behaviour because you are reading from an uninitialized B.