"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 .

Answer 2

After you have success downloaded and unzipped OpenCV sources from sources you need create simple command-file install.sh. For example, your working dir will be /home/user/myopencv

So /home/user/myopencv/install.sh will be contain next code:

#!/bin/bash

rm CMakeCache.txt
mkdir build
cd build
cmake .. -DCMAKE_BUILD_TYPE=RELEASE -DCMAKE_INSTALL_PREFIX=/usr/local 
make
make install
make clean

Next

chmod 777 install.sh
./install.sh

And after the all you will get those executable files:

root@cartman:/usr/local/bin# ls -las | grep opencv
 32 -rwxr-xr-x  1 root root   29888 апр 20 18:10 opencv_annotation
244 -rwxr-xr-x  1 root root  247608 апр 20 18:10 opencv_createsamples
244 -rwxr-xr-x  1 root root  247504 апр 20 18:10 opencv_haartraining
 20 -rwxr-xr-x  1 root root   18600 апр 20 18:10 opencv_performance
288 -rwxr-xr-x  1 root root  294592 апр 20 18:10 opencv_traincascade
 16 -rwxr-xr-x  1 root root   14288 апр 20 18:10 opencv_version
 60 -rwxr-xr-x  1 root root   61040 апр 20 18:10 opencv_visualisation

Enjoy!