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# CopyStringDescriptor

Returns a string descriptor from the device.

```
virtual const IOUSBStringDescriptor * CopyStringDescriptor(uint8_t index, uint16_t languageID);
```

## Parameters

`index`

The descriptor index value. This parameter corresponds to the low byte of `wValue` of the `SET_DESCRIPTOR` control request (USB 2.0, section 9.4.8).

`languageID`

The descriptor language ID. This parameter corresponds to the `wIndex` value of the `SET_DESCRIPTOR` control request (USB 2.0, section 9.4.8).

## Return Value

A pointer to the descriptor, if found. It’s your responsibility to free the returned descriptor.

## Discussion

This method searches the descriptor cache for the specified descriptor. If the descriptor isn’t in the cache, the method retrieves it from the device using a `GET_DESCRIPTOR` control request (USB 2.0, section 9.4.3) and adds it to the cache. When making a `GET_DESCRIPTOR` control request, this method acquires the service’s workloop lock and may call <doc://com.apple.documentation/documentation/kernel/iocommandgate/1573818-commandsleep>.

---

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