Running multiple versions of OpenCV on the same computer

Question

My computer is running Ubuntu-16.04-LTS and OpenCV-2.4.13 is already installed on it. However, I would like to use the functionalities of newer versions of OpenCV, such as OpenC

Answer 1

I have a working CMakelists.txt for almost the same configuration as you describe except that I am running a dauntingly old Ubuntu 12.04 (its not my own computer).

I believe your problem comes from this line:

find_package(OpenCV REQUIRED)

Which gives you access to your distribution's OpenCV 2.4. Then you are linking against the manually installed 3.2.x version. So problems arise as soon as the interface of a function you use has changed between the two version. Your first piece of code run by chance I think.

Here is my CMakeList.txt:

cmake_minimum_required(VERSION 2.8)
project(demo)

find_package(OpenCV 3.2 REQUIRED PATHS "/path/to/OCV3.2/install/dir/")

include_directories(${OpenCV_INCLUDE_DIRS})
add_executable(main main.cpp)
target_link_libraries(main ${OpenCV_LIBS})

If you do not want to commit to your repository the hardcoded path to your install of OpenCV 3.2 you can refine this CMakeList.txt by changing the find_package line to:

if(DEFINED ENV{OPENCV_INSTALL_DIR})
    find_package(OpenCV 3.2 REQUIRED PATHS $ENV{OPENCV_INSTALL_DIR})
else()
    message("OPENCV_INSTALL_DIR not set, searching in default location(s)")
    find_package(OpenCV 3.2 REQUIRED)
endif(DEFINED ENV{OPENCV_INSTALL_DIR})

Then you just have to define the variable OPENCV_INSTALL_DIR before running cmake. I do that by exporting it from my .bashrc