How to initialize a const field in constructor?

Question

Imagine I have a C++ class Foo and a class Bar which has to be created with a constructor in which a Foo pointer is passed, and this pointer is meant to remain immutable in the Bar instance lifecycle. What is the correct way of doing it?

In fact, I thought I could write like the code below but it does not compile..

class Foo;  class Bar { public:     Foo * const foo;     Bar(Foo* foo) {         this->foo = foo;     } };  class Foo { public:   int a; }; 

Any suggestion is welcome.

Answer 1

You need to do it in an initializer list:

Bar(Foo* _foo) : foo(_foo) { } 

(Note that I renamed the incoming variable to avoid confusion.)

Answer 2

I believe you must do it in an initializer. For example:

Bar(Foo* foo) : foo(foo) { } 

As a side note, if you will never change what foo points at, pass it in as a reference:

Foo& foo;  Bar(Foo& foo) : foo(foo) { }