> On Apr 25, 2017, at 2:57 PM, Rick Mann via swift-users
> <[email protected]> wrote:
>
> I'm trying to pass a Data of allocated size to a C function for it to fill in:
>
>
> lib_example_call(_ params: UnsafePointer<lib_call_params_t>!, _ data:
> UnsafeMutableRawPointer!)
>
> ...
> {
> self.dataBuffer = Data(capacity: BufferSizeConstant)
If you want to create a buffer with a given count you should use Data(count:
Int), the method you are using just reserves a given capacity. (from what I can
tell from your code that is likely what you really want)
>
> var params = lib_call_params_t();
> params.data_capacity = BufferSizeConstant;
>
> self.dataBuffer?.withUnsafeMutableBytes
> { (inBuffer) -> Void in
> lib_example_call(¶ms, inBuffer)
> }
> }
>
> I later get called back by the library with a size value of the actual data
> it got. self.dataBuffer is a var. I set self.dataBuffer?.count = result size,
> which is a reasonable value.
>
> Unfortunately, the resulting buffer is all zeros. The data generated by the
> call is definitely not all zero, and a C example program using the same
> library works correctly.
>
> So, I think there's something wrong in the way I'm making the call.
>
> Can anyone please enlighten me? Thanks!
>
> --
> Rick Mann
> [email protected]
>
>
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