Trouble using engEvalString to execute user-created functions

I'm trying to use the Matlab Engine from a C program to execute a function (.m file) that I've written. I can compile my code and execute built-in Matlab functions, but my function isn't being executed. It's not crashing or anything; it's as if my function is being skipped over. I used engEvalString to add the path to the .m file I'm running, i.e,

engEvalString(ep,"addpath('C:\My Matlab Code')" )

but still nothing happens.

What am I missing?