Call an IOUSBDeviceInterface function on an obj-c object instead of a C structure

Question

Let's say I want to close an USB device. Here is a C structure representing the USB device:

struct __USBDevice {

uint16_t idProduct;
io_service_t usbService;
IOUSBDeviceInterface **deviceHandle;
IOUSBInterfaceInterface **interfaceHandle;
Boolean open;

};

typedef struct __USBDevice *USBDeviceRef;

Here is the code to close the device:

// device is a USBDeviceRef structure
// USBDeviceClose is a function member of IOUSBDeviceInterface C Pseudoclass

(*device->deviceHandle)->USBDeviceClose(device->deviceHandle);

Now imagine that the device properties are declared in an obj-c class

@interface Device : NSObject {

NSNumber idProduct
io_service_t usbService;
IOUSBDeviceInterface **deviceHandle;
IOUSBInterfaceInterface **interfaceHandle;
BOOL open;
}

@end

How would I do to call USBDeviceClose() ?

score 1 · Accepted Answer · answered Jul 11 '12 at 02:42

1

There are two ways. You can either model your class similar to a struct, and add @public above your declarations (that way the syntax won't change) or you can add a Close method to your interface which will do the same logic internally (but without the need to dereference device of course).

answered Jul 11 '12 at 02:42

borrrden

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Could you provide a quick code example for the first way ? Thank you. – b1onic Jul 11 '12 at 02:45
I already did, simply add `@public` above all your iVars. Then you can access them like this `device->idProduct` etc. – borrrden Jul 11 '12 at 02:48

score 0 · Answer 2 · answered Jul 11 '12 at 03:11

0

No need to be redundant. Ivars can be structs.

@interface Device : NSObject {

USBDeviceRef deviceRef;
}

@end

#implementation Device

- (void) close {
USBDeviceClose(deviceRef->deviceHandle);
}

answered Jul 11 '12 at 03:11

NSResponder

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Haven't you forget (*deviceRef->deviceHandle)-> just before USBDeviceClose ? – b1onic Jul 11 '12 at 03:39

Call an IOUSBDeviceInterface function on an obj-c object instead of a C structure

2 Answers2