Qt error: LNK1181: cannot open input file 'debug\main.obj'

Question

Qt creator was working well, but suddenly shows a problem error: LNK1181: cannot open input file \'debug\\main.obj\'.
This problem shows always with any typ

Answer 1

What worked for me:

1. Close the Qt Creator
2. Delete the [filename].pro.user file in your project directory
3. Open the project again and let Qt configure itself

Generally whenever I encounter an error like this, this is one of the first things I do as it solves a lot of problems with Qt.

Edit: This will of course reset your project build location.

Answer 2

The problem has been solved.

The cause of the problem was when creating a new project (GUI or Console), all source files that belong to this new project take a wrong extension ex: main.cp, but the correct extension is supposed to be ex: main.cpp. And when change all the source files extension from .cp to .cpp worked fine.

Or change the default source file extension from [Tools -> Option -> C++].