lvalue - Get the address of an Objective-c property (which is a C struct)

Question

I have an Objective-C class which contains a C-style struct. I need to call a C function passing a pointer to this object member (a.k.a. property). For the life of me, I can't figure out how to get the address of this C struct. Using the traditional & operator to get the address, I'm getting an LValue compiler error.

typedef struct _myStruct
{
   int aNumber;
}MyStruct, *pMyStruct;

@interface MyClass : NSObject {
    MyStruct mystruct;
}
@property (readwrite) MyStruct myStruct;
@end

The following code results in a compiler error:

MyClass* myClass = [[MyClass alloc] init];

MyStruct* p = &(myClass.myStruct);

How do I get a pointer to the myStruct member of the myClass object?

Answer 1

There are often pretty good reasons to do what the original post is asking, given that Objective-C apps often have to work with C/C++ API's that take pointers to structs and similar types, but in a Cocoa app you'll often want to store such data in Objective-C classes for data management, collection in arrays and dictionaries, etc.

Though this question has been up for awhile I don't see the clear answer, which is: you can have a method that returns the address of the data that's backing your property, but in that method don't use "self" or it will go through the accessor and still not work.

- (const MyStruct*) getMyStructPtr
{
    return &mystruct;
}

Note that I'm using the declared property from the OP, but not referencing it as self.mystruct, which would generate a compiler error (because that invokes the synthesized getter method).