CMake – problem with adding opencv

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1

Let me introduce my problem. I have a project and I’m using git to maintain it. I added opencv as submodule:
git submodule add https://github.com/opencv/opencv.git external/opencv
In my top level cmake I added:

add_subdirectory(external/opencv)
find_package(OpenCV REQUIRED)
target_link_libraries (my_target ${OpenCV_LIBRARIES})
target_include_directories(my_target 
    PUBLIC ${OpenCV_INCLUDE_DIRS})

And run:

cmake -S . -B out/build

And I got error:

CMake Error at CMakeLists.txt:10 (find_package):
Could not find a package configuration file provided by “OpenCV” with any
of the following names:

OpenCVConfig.cmake
opencv-config.cmake

Add the installation prefix of “OpenCV” to CMAKE_PREFIX_PATH or set
“OpenCV_DIR” to a directory containing one of the above files. If “OpenCV”
provides a separate development package or SDK, be sure it has been
installed.

If I remove find_package from cmake, then cmake runs without problems, but when I try to build, then I get error of including opencv in main.cpp of my_target:

#include <opencv2/opencv.hpp>

I get error that it cannon find the header:

fatal error: opencv2/opencv.hpp: No such file or directory
    3 | #include <opencv2/opencv.hpp>

Intelisense seems to have no problems at all, I can navigate into that header from the editor.
I’m using Ubuntu 22.

2

no idea, what you intended by using a git submodule, however, this is the src code only ! you need to build the opencv libs before, and point OpenCV_DIR to the install dir

1 Like
4

I get it, but I need to configure cmake first and then run build, but it already complains at cmake configuration step. What I want to do is not to install opencv somewhere, but compile it in my project and then link it to my code that it needs it.

I commented out everythin except opencv in my cmake and I can configure and build it actually. I think my problem is most likely related to cmake build and link order than opencv itself…

EDIT: Ok, so I built opencv for sure and then added it to the project. This cmake configuration works:

add_subdirectory(external/opencv)
target_include_directories(my_target 
    PUBLIC ${OpenCV_INCLUDE_DIRS})    
target_link_libraries (my_target ${OpenCV_LIBRARIES})

But in my_target I can’t include:
#include <opencv2/opencv.hpp>

It complains:

main.cpp:3:10: fatal error: opencv2/opencv.hpp: No such file or directory
    3 | #include <opencv2/opencv.hpp>

If I add this to cmake:
find_package(OpenCV REQUIRED)

I got this cmake error from the original post. Cmake documentation doesn’t say anything about setting OpenCV_DIR, which path should I set to it?

5

I tried exactly the same steps with different library (glfw) and it works perfectly fine.

In terminal:
git submodule add <link> external/glfw

Added to cmake:

add_subdirectory(external/glfw)
target_include_directories(my_target
    PUBLIC external/glfw/include)
target_link_libraries(my_target
    glfw)

In terminal once again:

cmake -S . -B out/build
cd out/build ; ./my_target/my_target

But it doesn’t work for opencv…

6

you have to. e.g. the include folder gets assembled during install (it does not exist else)

you can still install to /home/frodo/ocv (CMAKE_INSTALL_PREFIX) or similar, point OpenCV_DIR at that later for your own prog, and delete it, ,when no more needed

useless / misleading