[CMake] A strange problem when I "rm -rf *" under project/build.

[Kermit Mei]

Hello, I create my project in the directory ~/project.

And then, I build it in ~/project/build as the following:

cd ~/project
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr ..
make
sudo make install

So far, everything of my program works well.

But, if I delete the files under ~/project/build/*,
My program will come back to the last version.

Why?