How to set the include path, #include "opencv2/opencv.hpp" - opencv

Question

I am trying to do Compiling With OpenCV section in this page: Installing Darknet
After I did OPENCV = 1, I tried to do re-make, so I did make in the darknet directory.
The directory is below.
(yolo) bash-3.2$ pwd
/Users/moray/darknet
(yolo) bash-3.2$ ls
LICENSE LICENSE.gpl LICENSE.v1 backup data libdarknet.a python src
LICENSE.fuck LICENSE.meta Makefile cfg examples libdarknet.so results
LICENSE.gen LICENSE.mit README.md darknet include obj scripts
and the result of the re-makaing is here.
(yolo) bash-3.2$ make
g++ -Iinclude/ -Isrc/ -DOPENCV `pkg-config --cflags opencv` -Wall -Wno-unused-result -Wno-unknown-pragmas -Wfatal-errors -fPIC -Ofast -DOPENCV -c ./src/image_opencv.cpp -o obj/image_opencv.o
/bin/sh: pkg-config: command not found
./src/image_opencv.cpp:6:10: fatal error: 'opencv2/opencv.hpp' file not found
#include "opencv2/opencv.hpp"
^~~~~~~~~~~~~~~~~~~~
1 error generated.
make: *** [obj/image_opencv.o] Error 1
So I thought include path could not reference opencv.hpp, I looked for the file and found it.
(yolo) bash-3.2$ ls ~/opt/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include/opencv2/opencv.hpp
/Users/moray/opt/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include/opencv2/opencv.hpp
Therefore I tried to change #include "opencv2/opencv.hpp" to "include "~/opt/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include/opencv2/opencv.hpp" in ./src/image_opencv.cpp
And the result is here.
(yolo) bash-3.2$ make
g++ -Iinclude/ -Isrc/ -DOPENCV `pkg-config --cflags opencv` -Wall -Wno-unused-result -Wno-unknown-pragmas -Wfatal-errors -fPIC -Ofast -DOPENCV -c ./src/image_opencv.cpp -o obj/image_opencv.o
/bin/sh: pkg-config: command not found
./src/image_opencv.cpp:7:10: fatal error:
'~/opt/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include/opencv2/opencv.hpp' file not found
#include "~/opt/anaconda3/pkgs/libopencv-3.4.2-h7c891bd_1/include/opencv2/opencv.hpp"
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
make: *** [obj/image_opencv.o] Error 1
I cannot understand why the error happens.
Please tell me your think.
============================================
os: macOS Catalina 10.15.1
(yolo) is a virtual environment in anaconda(3)
opencv was installed by pip command in (yolo)
all the packages by pip command in (yolo):
(yolo) bash-3.2$ pip list
Package Version
--------------------- -------------------
certifi 2019.11.28
numpy 1.17.4
opencv-contrib-python 4.1.2.30
opencv-python 4.1.1.26
pip 19.3.1
setuptools 42.0.2.post20191203
wheel 0.33.6
gcc:
(yolo) bash-3.2$ gcc --version
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
Apple clang version 11.0.0 (clang-1100.0.33.12)
Target: x86_64-apple-darwin19.0.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Answer 1

This error explains it pkg-config: command not found. In order to use OpenCV in YOLO, you have to install OpenCV that works for C or C++ program, not Python. You probably installed opencv using pip for Python. Follow these steps in one of these links to install opencv : this or this or other tutorial.
After that, to check whether you have installed OpenCV correctly and can be used in C program, run this command :
pkg-config --modversion opencv
If it doesn't show anything or shows wrong version, try to reinstall OpenCV OR it is possible that your machine doesn't locate opencv version correctly.
So add command to your ~/.bashrc for example :
vim ~/.bashrc
export PKG_CONFIG_PATH=/home/user/installation/OpenCV-3.4.0/lib/pkgconfig
source ~/.bashrc
Notes : Change the path according to your opencv installation directory that contains opencv.pc