How can I compile c++ files created with the mex.h library from the command line?

I have some c++ files that are intended to be compiled with mex through matlab from an open source repository. While they work just fine in matlab, I have to read in information from a file format that matlab doesn't deal with easily, so I would like to recompile the c++ files with a standard c++ compiler from the command line. Is there an easy way to do this? I've tried using g++ and it throws errors when it encounters the mex library.

Thanks!

[Harsheel]

Can you clarify the following questions?

1. What are these C++ files, do they contain mexFunction in them or are they general C++ files?
2. What do you mean by "they work just fine in matlab"? C++ files cannot be directly executed in matlab.
3. What is the command you use with g++ and what is the error?
4. What is the reason you need mex libraries?