linux - "In-source builds are not allowed" in cmake

Question

I'm new to cmake, and I'm only using it to install opencv on my ubuntu linux. Here's the command I ran:

"cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/home/jinha/OCV/source"

Then it returns the error:

"FATAL: In-source builds are not allowed.
You should create separate directory for build files."

My current directory, /home/jinha/OCV/build/opencv, does contain the CMakefiles.txt file, so that's not the problem. I tried to change the directory in my command, but they all raise the same error. I saw the other answers on this issue, so I erased CMakeFiles folder and CMakeCache.txt file every time before I ran the command, but none of them worked. Thanks.

Answer 1

It wants you to create a separate build directory (anywhere), and run cmake there. For example:

mkdir my_build_dir
cd my_build_dir
rm ../CMakeCache.txt
cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/home/jinha/OCV/source

Note the .. in this example telling cmake where to look for the source.

In case you didn't remove CMakeCache.txt before building again, it will still show this error. So, please remember to delete CMakeCache.txt first before running cmake.