XCode 4, intellisense with C files

I have an Objective-C project and I imported some c libraries 开发者_运维问答such as box2d. When I write out "b2V". the menu pops up for b2Vector. But if I declare variables of C types, it doesn't auto complete when I try to use them. Nor if I do "body->..."

Is it possible to make this work in XCode 4