C++ constructor initialization reference assignment

Question

I am sure this question has been asked before. But I cannot seem to find the exact answer that I am looking for. Basically I am trying to create an object of the class as a member of the other class and pass one of the members by reference to the owned object through the constructor. Sometimes this seems to work, other times I get a random value.

I think that I am not understanding some rudimentary rule of initialization order

Here is the code example:

class Foo
{
public:
    Foo();
private:
    int b;
    Bar c;
};

class Bar
{
public:
    Bar(int& parm);
private:
    int& b_ref;
};

Foo::Foo(): b(0), c(b)
{}

Bar::Bar(int& parm): b_ref(parm)
{}

What I want is for c to own a reference to b and be able see the value as it changes.

Should I not use the initialization list in this case?

Mankarse · Accepted Answer · 2013-03-18 04:43:05Z

3

The rule is that objects are initialised in the order of their declaration in the class. In this case, it means that b is initialised before c, so this code should always work correctly.

If you swapped the order of the b and c members, then the int referenced by param would not yet be initialised in the constructor of Bar.

answered Mar 18, 2013 at 4:43

Mankarse

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1 Comment

MadOgre Over a year ago

Yes I just realized that my actual code had the members swapped! Thank you that was exactly the problem.

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