Objective C in C++ – Out of Scope

Question

Hello,

I have a little problem with the WOsclib. Not particularly with the library, it's more the callback function. The listen to specific osc commands i have to put up some callback method like

void TheOscStartMethod::Method(
                          const WOscMessage *message,
                          const WOscTimeTag& when,
                          const TheNetReturnAddress* networkReturnAddress)
{
    std::cout << "Got the start signal";
    start.alpha = 1.0;
}

start is IBOutlet UIImageView.

But the compiler says me, that start is out of scope. If I try to access start in obj-c code, it works like it should.

How can i get my Objective C Objects into the c code or at least call a objective-c function.

Thank you

Answer 1

Make the file an objective C++ file with extension .mm Then you can call object C and C++ objects in the same code.

XCode will call the correct compiler from the file extension (ie adding -x objective-c++ to the compile command)

Not that C++ and objective C are different languages and do not understand each others objects so to move data between them you will need to convert the data to a C type e.g. void, char int and pointers to them.

Answer 2

It sounds like start is an instance variable belonging to some Objective-C object and you're trying to access it just by writing its name from a C++ object. If this is the case, it should be pretty obvious why it won't work: The C++ object doesn't know anything about start. The solution is to somehow give the C++ object a reference to the Objective-C object that owns start.

Answer 3

You'll have to make the start object available to your other code.

You can pass it, you can pass the portions you'll be using, you can create an API for the two code bases to use. There are other options as well, all depending on precisely how you wish to use the various objects

Answer 4

The Solution:

I don't know if this is the best way to do it, but it works.

There must be an empty c object, which later will become our objective c object that holds all the stuff we want to access.

static gsSearchForIp* delegate = NULL;

We must define a function to set the objective c object

void setCallbackDelegate(gsSearchForIp* del)
{
    delegate = del;
}

And then call it. ( I called it in the initWithFrame method)

setCallbackDelegate(self);

Now i can call a method with [delegate methodName:firstPara] in my c++ method. In this function i have access to all my stuff that I need from the gsSearchForIp class.