Hello Luís,
Am 26.08.2011 um 01:20 schrieb Luís Oliveira:
> Hello Frank,
>
> On Thu, Aug 25, 2011 at 6:19 PM, Frank Goenninger <f...@me.com> wrote:
>> In the sample code from Apple the C function is called like this:
>>
>> typedef struct MyPrivateData {
>> io_object_t notification;
>> IOUSBDeviceInterface **deviceInterface;
>> CFStringRef deviceName;
>> UInt32 locationID;
>> } MyPrivateData;
>
> Why is deviceInterface a pointer to a pointer?
Because Apple designed the interface to calls like GetLocationID in IOKit like
this:
kr =
(*privateDataRef->deviceInterface)->GetLocationID(privateDataRef->deviceInterface,
&locationID);
Here I need to pass the address of a pointer to IOUSBDeviceInterface struct ...
This:
IOReturn (*GetLocationID)(void *self, UInt32 *locationID);
is part of
typedef struct IOUSBDeviceStruct {
...
} IOUSBDeviceInterface;
So, it's actually the address of a pointer to a IOUSBDeviceInterface struct.
I have defined this as:
(defcstruct IOUSBDeviceStruct
(_reserved :pointer)
(QueryInterface :pointer)
(AddRef :pointer)
(Release :pointer)
;; Function Pointers
(CreateDeviceAsyncEventSource :pointer)
(GetDeviceAsyncEventSource :pointer)
(CreateDeviceAsyncPort :pointer)
(GetDeviceAsyncPort :pointer)
(USBDeviceOpen :pointer)
(USBDeviceClose :pointer)
(GetDeviceClass :pointer)
(GetDeviceSubClass :pointer)
(GetDeviceProtocol :pointer)
(GetDeviceVendor :pointer)
(GetDeviceProduct :pointer)
(GetDeviceReleaseNumber :pointer)
(GetDeviceAddress :pointer)
(GetDeviceBusPowerAvailable :pointer)
(GetDeviceSpeed :pointer)
(GetNumberOfConfigurations :pointer)
(GetLocationID :pointer)
(GetConfigurationDescriptionPtr :pointer)
(GetConfiguration :pointer)
(SetConfiguration :pointer)
(GetBusFrameNumber :pointer)
(ResetDevice :pointer)
(DeviceRequest :pointer)
(DeviceRequestAsync :pointer)
(CreateInterfaceIterator :pointer))
(defctype IOUSBDeviceInterface IOUSBDeviceStruct)
So, IOKit lib allocates the memory for this struct and the pointer passed in
via the pointer address is then pointing to this memory block. Or that's at
least how I understood it ...
Thanks!
Frank
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