http://blog.dlib.net/2016/06/a-clean-c11-deep-learning-api.html
Dlib is a modern C++ toolkit containing machine learning algorithms and tools for creating complex software in C++ to solve real world problems. It is used in both industry and academia in a wide range of domains including robotics, embedded devices, mobile phones, and large high performance computing environments.
Source code: https://github.com/davisking/dlib