Besides the already-mentioned pytorch and tensorflow bindings, http://dlib.net/ http://dlib.net/ is an option if C++ is really a hard requirement. It is opinion

Besides the already-mentioned pytorch and tensorflow bindings, http://dlib.net/ http://dlib.net/ is an option if C++ is really a hard requirement. It is opinionated and incomplete, basically being a one-man-show, but it has some weird-but-cool ideas like each neural network topology having its own template type.