C ++私有拷贝构造函数问题

Question

I am building a small C++ app and I was looking to make a private copy constructor for my reference holder.

When I use my class in my main, everything works, but when I try to test it with Google Test, I get an error stating that my copy constructor is private

TEST (Library, constructorParams) {
    Library lib = Library("my Library");
    ASSERT_EQ("my Library", lib.getNom());
}

Library.h (there is no definition for the copy constructor and the assignation operator in my .cpp)

class Library {
public:
    ...
private:
    ...

    Library (const Library& obj);
    Library & operator=(const Library& obj);
};

Why am I getting an error for my private copy constructor (might it be a bad usage in my Tests?)?

Answer 1

Here

Library lib = Library("my Library");

you are semantically performing a copy construction from a temporary object constructed on the RHS. Even of the compiler might optimize copies out, the copy constructor needs to be publicly accessible.

Try this instead:

Library lib("my Library");

See more on copy initialization .

Answer 2

Library lib = Library("my Library");

On this line you try to copy-construct an object of type Library , but this can't be done as its copy-constructor is private. You should instead do this:

Library lib("my Library");

Answer 3

You are calling the copy constructor from this line of code

Library lib = Library("my Library");

And you have defined it as a private method of that class.

That operation is not related to a call to the assignment operator (which you mention in the question), this is more clear if you consider its equivalent:

Library lib(Library("my Library"));  // Here the invocation of the copy 
                                     // constructor is more explicit

With the code in this format, it is also more clear that there's no need to first create the object in a temporary than call the copy constructor to create another instance of that object.

The correct way should be:

Library lib("my Library");