One more thing is that where in ubuntu is file_sink.cc or the C++ files of blocks present?
I searched the whole computer for '.cc' and found no .cc gnu radio block file.
I think I can easily change the C++ code to solve this problem.
Please don't recommend adding a new block, because I have tried that 2 or 3 times and it just does not work.
There are different errors everytime I try to add a new block, sometimes gnu radio just doesn't pick it up etc.