do_createinstance xpcom

Question

i use this code nsCOMPtr file = do_CreateInstance("@mozilla.org/file/local;1", &rv);

it says error C3861: 'do_CreateInstance': identifier not found

Answer 1

This is not a real question. You obviously haven't set up the build correctly and it's hard to guess the full list of things you could have done wrong, short of writing a step-by-step tutorial.

Find an example project that does what you need and see how it's set up.