This is a simple 3-layer BP net implemented in C++.
There is an example to load train data and train BP net to fit the sin function.
take windows for example, follow cmd commands below and run the vs project generated, where OpenCV_DIR points to your own opencv installation path.
cd %bpnet_root%
mkdir build
cd build
:: if no opencv change it to: cmake .. -G "Visual Studio 15 2017 Win64
cmake .. -G "Visual Studio 15 2017 Win64" -DUSE_OPENCV=ON -DOpenCV_DIR=D:\opencv-3.3.0\build