With C you can reach only a partial decompiling due to the complexities caused by the optimizations in the compiler. The source code can have many statements that are simply optimized away when it is complied.
With C++, well, sorry, it is impossible. How on the earth you can reach the source code of a STL vector or a Boost smart pointer by looking at the machine code? They are already lost in the first compilation phases and even dont make it to the backend....