MATLAB arbitrary code execution

Question

I am writing an automatic grader program under linux. There are several graders written in MATLAB, so I want to tie them all together and let students run a program to do an assignment, and have them choose the assignment. I am using a C++ main program, which then has mcc-compiled MATLAB libraries linked to it.

Specifically, my program reads a config file for the names of the various matlab programs, and other information. It then uses that information to present choices to the student. So, If an assignment changes, is added or removed, then all you have to do is change the config file.

The idea is that next, the program invokes the correct matlab library that has been compiled with mcc. But, that means that the libraries have to be recompiled if a grader gets changed. Worse, the whole program must be recompiled if a grader is added or removed. So, I would like one, simple, unchanging matlab library function to call the grader m-files directly. I currently have such a library, that uses eval on a string passed to it from the main program.

The problem is that when I do this, apparently, mcc absorbs the grader m-code into itself; changing the grader m code after compilation has no effect. I would like for this not to happen. It was brought to my attention that Mathworks may not want me to be able to do this, since it could bypass matlab entirely. That is not my intention, and I would be happy with a solution that requires a full matlab install.

My possible solutions are to use a mex file for the main program, or have the main program call a mcc library, which then calls a mex file, which then calls the proper grader. The reason I am hesitant about the first solution is that I'm not sure how many changes I would have to make to my code to make it work; my code is C++, not C, which I think makes things more complicated. The 2nd solution, though, may just be more complicated and ultimately have the same problem.

So, any thoughts on this situation? How should I do this?

Answer 1

Don't make this a mex function.

Use a regular m-file that has to be executed in matlab. If you don't want to launch matlab first, write a bat file. I believe -r or -m runs a given command (you will have to cd to the correct directory before running you ml function).

To compile c++ code using mex first install visual studio. Then run (in matlab) mex -setup. Select "locate installed compilers" or some such, and then select your compiler from the list. Now mex will compile c++ code.

Answer 2

Using the MATLAB Engine to Call MATLAB Software from C/C++ and Fortran Programs

Answer 3

You seem to have picked the most complicated way of solving the problem. Here are some alternatives:

1. Don't use C/C++ at all -- Write a MATLAB program to display the menu of choices (either a GUI for a simple text menu in the MATLAB command window) and then invoke the appropriate MATLAB grading programs.

2. Write your menu program in C/C++, but invoke MATLAB using a -r argument to run a specific grading program (to speed up the startup times, use the -nodesktop, -nojvm or -nodisplay options as appropriate). However, note that MATLAB will be started anew on each menu selection.

3. Write your menu program in C/C++ and start MATLAB using the popen command (this sets up a pipe between your C++ program and the MATLAB process). After a menu selection by the user:

   • your C++ program writes the name of the MATLAB program (and any parameters) to the pipe.
   • On the MATLAB side, write a MATLAB program to a blocking read on that pipe. When it reads a command, it invokes the appropriate MATLAB function.
   • You could also use named pipes. See this MATLAB newsgroup thread for more information.

Update: Option #3 above is effectively how the MATLAB engine works, so you are probably better off using that directly.