How to use functions?

I开发者_如何学C define a function in a separate .m file and then when I want to use it (in other implementation files), I just don't know what to import, to actually see it.

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You need to create a header that declares the function and import that. So if you have the following file:

MyFavoriteTransformer.m

NSString *MyFavoriteTransformer() {
    return @"Hot Rod"; // Come on -- he's awesome!!!!
}

You'll want to have a corresponding file like this:

MyFavoriteTransformer.h

NSString *MyFavoriteTransformer();

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Assuming that you already have a matching .h file for your .m file, you just need to add #import "MyUtilityClass.h" to the header file of whatever other class you want to use your class from.