C / C++ / MFC

// You will need the forward declares
class USDB;
class HCD;

class USBD {
public:
	void ConnectHCD (HCD* hcd);   // Connect a HCD pointer into a USBD
    void SomeFunction (void);    // Some test function

	HCD* ConnectedHCD; // Pointer to connected buddy class it will be NULL after construction
};

class HCD {
public:
	void ConnectUSBD (USBD* usbd); // Connect a USBD into a HCD

	USBD* ConnectedUSBD; // Pointer to connected buddy class it will be NULL after construction
};

/* Simply hold given HCD pointer .. allows connectedHCD to be private if you want */
void USBD::ConnectHCD (HCD* hcd) {
	ConnectedHCD = hcd;
}

/* Our test function */
void USBD::SomeFunction (void){ 
}

/* Simply hold given USBD pointer ... allows connectedUSBD to be private if you want */
void HCD::ConnectUSBD (USBD* usbd) {
	ConnectedUSBD = usbd;
}

// SO LETS USE IT IN YOUR CODE

/* First we create our class objects */ 
USBD usbd;    // Create a usbd
HCD hcd;      // Create a hcd

/* Then we connect them */
usbd.ConnectHCD(&hcd);  // Connect the created hcd as a pointer into usbd
hcd.ConnectUSBD(&usbd); // Connect the created usbd as a pointer into hcd

// Done you may now freely use the each class inside the other using the pointer
// Dead simple and get around all the mess you are doing .. so lets do one
hcd.ConnectedUSBD->SomeFunction();  // Just call it via the the pointer

void USBD:: SomeFuncThatNeedsHCD (HCD* hcd){
    hcd->SomeHCDFunction();
}

static void SomeStaticCodeWhoAccessHCD (HCD* hcd){
    hcd->SomeHCDFunction();
}

PSOMECLASS* TheClassObject = NULL;

static void InterruptComesInHere (void){
   if (TheClassObject) {                 // Make sure class/object has been set otherwise interrupt just returns
       TheClassObject->CallSomeMethod(); // Send interrupt into class/object if set
   }
}

class IDE_USBD;
class IDE_HCD;

class IDE_USBD {
	// ... this classes data and at least prototypes to functions

public:
	// lets do a prototype
	int Hello(void);
};


class IDE_HCD {
	// ... this classes data and at least prototypes to functions
};

// Class IDE_ILI9341 can now use the above two classes as the compiler can size them
class IDE_ILI9341
{
public:
	IDE_HCD hcd;
	IDE_USBD usbd;
};


// we can put the code for IDE_USBD prototype down here
int IDE_USBD::Hello(void) {

}

class IDE_USBD;
class IDE_HCD;

class IDE_ILI9341
{
public:
	IDE_HCD* hcd;
	IDE_USBD* usbd;
};

class IDE_USB {
};

class IDE_HCD {
};

 hcd = new IDE_HCD ( /* .. parameters it takes ..*/ );
usbd = new IDE_USB ( /* .. parameters it takes ..*/ );

class IDE_USBD;
class IDE_HCD;

class IDE_ILI9341
{
public:
  IDE_HCD hcd;
  IDE_USBD usbd();
  ...

int i;                               // You created an integer type called i
double d;                            // You created a double called d
DownloadManager objDownloadManager;  // You created a DownloadManager called objDownloadManager

int* i;                               // You created a pointer to an integer type called i
double* d;                            // You created a pointer to a double type called d
DownloadManager* objDownloadManager;  // You created a pointer to a DownloadManager type called objDownloadManager