const reference must be initialized in constructor base/member initializer list

问题

I am trying to block access to the default constructor of a class I am writing. The constructor I want others to use requires a const reference to another object. I have made the default constructor private to prevent others from using it. I am getting a compiler error for the default constructor because the const reference member variable is not initialized properly. What can I do to make this compile?

class CFoo
{
public:
    CFoo();
    ~CFoo();
};

class CBar
{
public:
    CBar(const CFoo& foo) : fooReference(foo)
    {
    }

    ~CBar();

private:
    const CFoo& fooReference;

    CBar() // I am getting a compiler error because I don't know what to do with fooReference here...
    {
    }
};

回答1:

don`t declare default constructor. It is not available anyway (automatically that it's) if you declare your own constructor.

class CBar
{
public:
    CBar(const CFoo& foo) : fooReference(foo)
    {
    }
private:
    const CFoo& fooReference;
};

fairly comprehensive explanation of constructors can be found here: http://www.parashift.com/c++-faq-lite/ctors.html

回答2:

The easiest way to create the default constructor you don't wanna use (that is the case with your constructor, is that right?) is just not defining it, that is:

class CBar
{
public:
    CBar(const CFoo& foo) : fooReference(foo)
    {
    }

    ~CBar();

private:
    const CFoo& fooReference;

    CBar();
};

In this case, it may be a little superfluous, because the compiler will not create a default constructor for a class with a reference member, but it's better to put it there in case you delete the reference member.

来源：https://stackoverflow.com/questions/3168238/const-reference-must-be-initialized-in-constructor-base-member-initializer-list

标签

c++

constructor

reference

initialization