Compiling opencv program cause gcc -I/usr/local/lib test.cpp test.cpp:1:10: fatal error: opencv2/core.hpp: No such file or directory

There is a error when compiling opencv program program simple includes #include <opencv2/core.hpp>

I compiled it with this command

 g++ test.cpp -o app `pkg-config --cflags --libs opencv`

compiling opencv in c++

This is full error

gcc -I/usr/local/lib test.cpp 
test.cpp:1:10: fatal error: opencv2/core.hpp: No such file or directory
    1 | #include <opencv2/core.hpp>

I compiled and install the opencv by looking at this page https://docs.opencv.org/2.4/doc/tutorials/introduction/linux_install/linux_install.html#building-opencv-from-source-using-cmake-using-the-command-line

The code is from https://docs.opencv.org/4.x/d3/d50/group__imgproc__colormap.html

Also my opencv so files are located at /usr/local/lib

Error also says

Perhaps you should add the directory containing `opencv.pc'
to the PKG_CONFIG_PATH environment variable

but I searched /usr directory there is no opencv.pc file

Update

Compiling program after updating my compile command This error throws

 $g++ -I/usr/local/include/opencv4/ test.cpp 
/usr/bin/ld: /tmp/ccuJvWgF.o: in function `main':
test.cpp:(.text+0xb4): undefined reference to `cv::imread(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
/usr/bin/ld: test.cpp:(.text+0xde): undefined reference to `cv::Mat::empty() const'
/usr/bin/ld: test.cpp:(.text+0x154): undefined reference to `cv::Mat::Mat()'
/usr/bin/ld: test.cpp:(.text+0x1a1): undefined reference to `cv::applyColorMap(cv::_InputArray const&, cv::_OutputArray const&, int)'
/usr/bin/ld: test.cpp:(.text+0x21d): undefined reference to `cv::imshow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, cv::_InputArray const&)'
/usr/bin/ld: test.cpp:(.text+0x254): undefined reference to `cv::waitKey(int)'
/usr/bin/ld: test.cpp:(.text+0x265): undefined reference to `cv::Mat::~Mat()'
/usr/bin/ld: test.cpp:(.text+0x274): undefined reference to `cv::Mat::~Mat()'
/usr/bin/ld: test.cpp:(.text+0x33d): undefined reference to `cv::Mat::~Mat()'
/usr/bin/ld: test.cpp:(.text+0x355): undefined reference to `cv::Mat::~Mat()'
collect2: error: ld returned 1 exit status
$ 

Update 2

when now compiling

g++ -L/usr/local/lib/libopencv_core.so -I/usr/local/include/opencv4/ test.cpp 

it throws this error. There are many opencv so files in /usr/local/lib do I need to include specific opencv so files to compile the code in the link

 in function `main':
test.cpp:(.text+0xb4): undefined reference to `cv::imread(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int)'
/usr/bin/ld: test.cpp:(.text+0xde): undefined reference to `cv::Mat::empty() const'
/usr/bin/ld: test.cpp:(.text+0x154): undefined reference to `cv::Mat::Mat()'
/usr/bin/ld: test.cpp:(.text+0x1a1): undefined reference to `cv::applyColorMap(cv::_InputArray const&, cv::_OutputArray const&, int)'
/usr/bin/ld: test.cpp:(.text+0x21d): undefined reference to `cv::imshow(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, cv::_InputArray const&)'
/usr/bin/ld: test.cpp:(.text+0x254): undefined reference to `cv::waitKey(int)'
/usr/bin/ld: test.cpp:(.text+0x265): undefined reference to `cv::Mat::~Mat()'
/usr/bin/ld: test.cpp:(.text+0x274): undefined reference to `cv::Mat::~Mat()'
/usr/bin/ld: test.cpp:(.text+0x33d): undefined reference to `cv::Mat::~Mat()'
/usr/bin/ld: test.cpp:(.text+0x355): undefined reference to `cv::Mat::~Mat()'
collect2: error: ld returned 1 exit sta