QT compiler is not very stable, and many times we compile successfully before, after add the code to compile error, but to change back to before the code to compile again is still can’t succeed, this is likely to be QT save error compiling information before but can’t automatic updates, it needs us to manually clear the wrong compilation of information at this time, the following methods gradually progressive, there is always a can solve, all bad!!!!!!!!!!
 
1. Delete the Debug and Release folders of the project
2. Delete ****. Pro. user file
C:\Users\” YourPath “\AppData\Local\QtProject\QtCreator\ Cache
C:\Users\” YourPath “\AppData\ QtProject\ QtCreator