How to initialize a const field in constructor?

c++ constructor constants ctor-initializer
puccio picture puccio · Sep 14, 2009 · Viewed 79k times · Source

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

Jim Buck picture Jim Buck · Sep 14, 2009

You need to do it in an initializer list:

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

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

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