Charles Hixson:

So... if C returns an int64_t and I declare it as an int32_t, will this cause problems?  What about if C returns an int32_t and I declare it as an int64_t?  Or *is* there a good way to handle this? (I think that there's an error code I could interrogate if I need to just ignore the result...but I don't know if I can do this in all cases.)

Take a look at this entertaining page:
http://dlang.org/phobos/std_stdint.html

Bye,
bearophile

-- 
Charles Hixson