CMake error when building OpenCV - CMakeLists not match

Question

I tried to build OpenCV 3.1.0 on my Raspberry Pi 2B. Unfortunetly, when I trying:

cmake -D CMAKE_BUILD_TYPE=RELEASE \\ -D CMAKE_INSTALL_PREFIX=/usr/lo

Answer 1

First, I hope you do run CMake outside your sources, in a separate directory. Not doing that is really not recommended

To understand the error message you have to know a little bit on how CMake works.

Basically, when you run

cd /path/to/opencv
mkdir build
cd build
cmake ..

CMake generates a cache in the build dir (It's a simple file named CMakeCache.txt). This file contains some information like:

• The path to the sources /path/to/opencv
• The path to the build dir /path/to/opencv/build
• The CMake Generator used (Ninja, Unix Makefiles ...)

If you ever re-run CMake and change one of these values, (by re-running cmake with different arguments, setting an other generotor or moving files), CMake will complain with this kind of message.

A good solution is then to delete the CMakeCache, or even the whole build dir to be safe.

Answer 2

The reason is you have used two version of cmake to generate the Makefile.

cd /path/to/opencv
rm -rf build
mkdir build
cd build
cmake ..

that will be work fine.

• Installing OpenCV 2.4.9 in Ubuntu 14.04 LTS http://www.samontab.com/web/2014/06/installing-opencv-2-4-9-in-ubuntu-14-04-lts/