Later I was able to get my program to compile on Visual C++ with absolutely no modification.
I was referring to the binary interface. What I'd want to do (and generally can with C) is compile a library with any compiler, and link it with any other code, with no recompiling.
You see this all the time with Unix, say; maybe Sun compiles a bunch of stuff with their C compiler, but you can easily link to what's in /usr/lib using GCC. But with C++, it's typical for the loader to not link C++ libraries that were built differently; and if you're really unlucky, the loader won't notice and instead you'll see subtle binary errors at runtime.