c++:error2019, unresolved external command blabla~

Summary of issues that occur for this reason:

1, the corresponding additional library is not included, note that the directory of the additional library is/

2, the function does not have a corresponding class, but the method is called in main with a class of objects.

In fact, when the error shows fun () as an unresolved external command, I F12 two options to choose, but I did not find-it is the function of this class, F12 is also given the CPP and H file in the definition of fun (). It is clear that the fun () method in the CPP file is not connected to the fun () declared in the header file class, causing the IDE to assume that there are two fun () methods.

3, if the constructor is a problem, pay attention to the formal writing of the constructor function. Declaration is different from other functions, it is a curly brace {}

c++:error2019, unresolved external command blabla~