[SOLVED] Having relevant .so and binaries inside the venv

Issue

I installed OpenCV using Anaconda, with the following command.

mamba create -n opencv -c conda-forge opencv matplotlib

I know that the installation is fully functional because the below works:

import cv2
c = cv2.imread("microphone.png")
cv2.imwrite("microphone.jpg",c)
import os
os.getpid() # returns 13249

Now I try to do the same using C++.

#include <opencv2/core.hpp>
#include <opencv2/imgcodecs.hpp>
#include <iostream>
using namespace cv;
int main()
{
    std::string image_path = "microphone.png";
    Mat img = imread(image_path, IMREAD_COLOR);
    if(img.empty())
    {
        std::cout << "Could not read the image: " << image_path << std::endl;
        return 1;
    }
    imwrite("microphone.JPG", img);
    return 0;
}

And the compilation:

> g++ --version
g++ (conda-forge gcc 12.3.0-3) 12.3.0
Copyright (C) 2022 Free Software Foundation, Inc.
...
> export PKG_CONFIG_PATH=/home/stetstet/mambaforge/envs/opencv/lib/pkgconfig
> g++ opencv_test.cpp `pkg-config --cflags --libs opencv4` 

When I run the above, g++ complains that I am missing an OpenGL.

/home/stetstet/mambaforge/envs/opencv/bin/../lib/gcc/x86_64-conda-linux-gnu/12.3.0/../../../../x86_64-conda-linux-gnu/bin/ld: warning: libGL.so.1, needed by /home/stetstet/mambaforge/envs/opencv/lib/libQt5Widgets.so.5, not found (try using -rpath or -rpath-link)

After some experimentation I discover that some of the libraries must be from /usr/lib/x86_64-linux-gnu, while others must be used from /home/stetstet/mambaforge/envs/opencv/lib/ (opencv is the name of the venv in use). The following yields an a.out which does what was intended:

> /usr/bin/g++ opencv_test.cpp `pkg-config --cflags --libs opencv4` -lpthread -lrt

The /usr/bin/g++ so that it can actually find libGL.so.1 as well as libglapi.so.0, libselinux.so.1, libXdamage.so.1, and libXxf86vm.so.1. Also, without -lpthread -lrt these libraries are used from the venv, which causes "undefined reference to `h_errno@GLIBC_PRIVATE'"

Now, I am very bothered by the fact that I now need to know which one of which library (and g++/ld) I should use. I thought package managers were supposed to handle the dependency mess for us!

Would there be any way to make the compilation command into something like

> g++ opencv_test.cpp `pkg-config --cflags --libs opencv4`

i.e. have all relevant files or binaries inside the venv? For example, is there a way to modify the mamba create command (see top) so that this condition is satisfied?

Note: I am tagging both Anaconda, Linux, and OpenCV because I have absolutely no idea what I can use to reach a solution.

Solution

You need pkg-config to also be in the env. The following should work:

mamba create -n opencv -c conda-forge opencv matplotlib pkg-config
mamba activate opencv
g++ opencv_test.cpp `pkg-config --cflags --libs opencv4` 

Answered By - MEE

Answer Checked By - David Marino (WPSolving Volunteer)