C++ – call a constructor from another constructor (do constructor chaining) in C++

cconstructor

As a C# developer I'm used to running through constructors:

class Test {
    public Test() {
        DoSomething();
    }

    public Test(int count) : this() {
        DoSomethingWithCount(count);
    }

    public Test(int count, string name) : this(count) {
        DoSomethingWithName(name);
    }
}

Is there a way to do this in C++?

I tried calling the Class name and using the 'this' keyword, but both fail.

Best Answer

C++11: Yes!

C++11 and onwards has this same feature (called delegating constructors).

The syntax is slightly different from C#:

class Foo {
public: 
  Foo(char x, int y) {}
  Foo(int y) : Foo('a', y) {}
};

C++03: No

Unfortunately, there's no way to do this in C++03, but there are two ways of simulating this:

  1. You can combine two (or more) constructors via default parameters:

    class Foo {
public:
  Foo(char x, int y=0);  // combines two constructors (char) and (char, int)
  // ...
};

  2. Use an init method to share common code:

    class Foo {
public:
  Foo(char x);
  Foo(char x, int y);
  // ...
private:
  void init(char x, int y);
};

Foo::Foo(char x)
{
  init(x, int(x) + 7);
  // ...
}

Foo::Foo(char x, int y)
{
  init(x, y);
  // ...
}

void Foo::init(char x, int y)
{
  // ...
}

See the C++FAQ entry for reference.

Related Topic