vs2015 Write MFC program grammatically correct but there is a grammatical error

Just getting started with MFC, a syntax error occurs when a single-document program is generated and the code is debugged, but the correct syntax is the place where the syntax error is
prompted , as shown in the figure below:

The place where the error is reported is as follows: this function code is to define a Doc function The pointer is defined to facilitate access to the content. In the previous debugging, no error was reported. Then I tried to comment some of the added code, but it still didn’t work. Then I was ready to rebuild the project, and then found that the header file had a problem:

each other in the header file Quoting, you will definitely get an error, just use it in the cpp file, you can put an introduction of the header file into the cpp file, and it's done!