Which is the difference between declaring a constructor private and =delete?

Question

For example, I want to declare a class but I want the client to not be able to use the copy constructor (or copy assignment operator)

Both of the following two does

Answer 1

If you are on C++11, use delete. The reason is that it makes the call explicit and the intent clear. You could still accidentally use a private constructor (e.g. in a restricted set of scopes), but the compiler will forbid you from ever using a deleted constructor.

One issue of the private constructor is that the class and friends can still use it -- this results not in access errors but link errors, which can be hard to trace back to the callsite.

If your necessary toolchains do not support deleted constructors (= delete), you should not define it (as seen in your question) -- only declare it and leave it undefined, e.g.: private: \n Track(const Track&);