Oh, I'm pretty sure I know exactly what you mean. I think google let me down by not leading me to that thread with my same error. Is there a function that will parse my .txt shader files and put them in a std::string?
No, but it's pretty easy to do yourself. There are many solutions, and which you choose probably doesn't matter in your situation (you don't need reading shader files to be blazing fast, as it's a one time thing and they're usually not massive files). I'd probably wrap it up in a function.
Also, just to nitpick a technicality, you don't need to parse your shader files (parsing has to do with syntactic analysis). You just need to read the source into memory so you can pass it on to OpenGL to compile the shader source.