[PATCH 15/15] api-ms-win-core-winrt-string: Implement a few HSTRING functions.

[Sebastian Lackner]

Hi Martin,

please note that besides functions like WindowsSubstring which implicitly manipulate the string buffer, there are also some functions for explicit string buffer management:

WindowsPreallocateStringBuffer - allocate a new string buffer with refcount 1
WindowsPromoteStringBuffer - create a new string based on an existing string buffer without incrementing refcount
WindowsDeleteStringBuffer - decrement the refcount of a string buffer

Of course there are a lot more internal functions, but I think it should give a rough idea of how everything works on Windows. If you need any help with implementing this feel free to ask, we're also interested in this functionality. ;)

Regards,
Sebastian

On 06.12.2014 17:26, Martin Storsjö wrote:
> Hi Michael,
> 
> On Sat, 6 Dec 2014, Michael Müller wrote:
> 
>> you are right that WindowsSubstring always creates a new backing buffer
>> (although it is not necessary), but there is also
>> WindowsDuplicateString. This function indeed uses the same backing
>> buffer as you can verify with this small sample code:
>> https://dl.dropboxusercontent.com/u/61413222/test-string.c
>>
>> The MSDN also explicitly mentions that the refcount is incremented in
>> this case:
>> "If string was created by calling the WindowsCreateString function, the
>> reference count of the backing buffer is incremented. If string was
>> created by calling the WindowsCreateStringReference function, the
>> Windows Runtime copies its source string to a new buffer and starts a
>> reference count, which means that newString is not a fast-pass string."
>> Source: http://msdn.microsoft.com/en-us/library/br224634(v=vs.85).aspx
>>
>> It is necessary to implement reference counting in order to be fully
>> compatible with the Windows implementation.
> 
> Oh, I see - I hadn't checked this particular function (yet).
> 
> Ok then, then it's clear where/how to hook up the reference counting. I'll see if I can get to attempting implementing this sometimes soon.
> 
> // Martin