You don't validate the C++ code, you validate the algorithm before you implement it with C++. You have an idea for an algorithm, write it down with TLA+. TLA+

You don't validate the C++ code, you validate the algorithm before you implement it with C++. You have an idea for an algorithm, write it down with TLA+. TLA+ tells you if you screwed something up. You refine the algorithm until TLA+ says it's okay now. You implement the refined algorithm with the programming language of your choice. Everything that happens from that point is outside of TLA+'s power.