So I've used plenty of STL functions which takes functors as parameters. For calculating set differences, for sorting vectors, etc. I'm in a situation where I'd like to write such a function ...

Surely, writing the function inline will be much more convenient, clean and easy to read. Of course, the lambda is not the only option. You can use functors, function objects, lambdas or function ...

So I have a C++ program that I'm refactoring from someone elses code. It has a File class object called File_C that's intended to handle all the file i/o for input files and put the data in files ...