How to call an Objective-C Method from a C Method?

In order for that to work, you should define the C method like this:

void cMethod(id param);

and when you call it, call it like this:

cMethod(self);

then, you would be able to write:

[param objcMethod];

In your cMethod.

This is because the self variable is a special parameter passed to Objective-C methods automatically. Since C methods don't enjoy this privilege, if you want to use self you have to send it yourself.

See more in the Method Implementation section of the programming guide.

I know your question is already answered by Aviad but just to add to the info since this is not unrelated:

In my case I needed to call an Objective-C method from a C function that I did not call myself (a Carbon Event function triggered by registering a global hotkey event) so passing self as a parameter was impossible. In this particular case you can do this:

Define a class variable in your implementation:

id thisClass;

Then in your init method, set it to self:

thisClass = self;

You can then call Objective-C methods from any C function in the class without the need to pass self as a parameter to the function:

void cMethod([some parameters]) {
    [thisClass thisIsAnObjCMethod];
}