On 15 November 2017 at 20:47, Esteban Lorenzano <estebanlm@gmail.com> wrote:

On 15 Nov 2017, at 09:36, Ben Coman <btc@openInWorld.com> wrote:

On 15 November 2017 at 17:27, Esteban Lorenzano��<estebanlm@gmail.com>��wrote:

> On 15 Nov 2017, at 02:05, Ben Coman <btc@openInWorld.com> wrote:
>
> What is the recommended way for a C basic type to be passed-by-reference to function wanting to use it for output.
> For example 'width' & 'height' here in this library unction...
>
> In Pharo...
>
>�� FFIOpaqueObject subclass: #FPDF_DOCUMENT
>
>�� FPDF_GetPageSizeByIndex__document: document
>�� page_index: page_index
>�� width: width
>�� height: height
>�� ^self ffiCall: #(int FPDF_GetPageSizeByIndex(
>�� FPDF_DOCUMENT *document,
>�� int page_index,
>�� FFIFloat64 * width,
>�� FFIFloat64 * height))

what you need to do here is to pass a ��buffer�� to contain the width and height:

testGetPageSizeByIndex
�� | document page_index widthBuffer heightBuffer width height result|
�� PDFium FPDF_InitLibrary.
�� document := PDFium FPDF_LoadDocument__file_path:�� helloPdf�� password: ''.
�� widthBuffer := ByteArray new: (FFIFloat64 typeSize).
�� heightBuffer := ByteArray new: (FFIFloat64 typeSize).

Thanks Esteban. That worked. However I needed a minor tweak...
�� widthBuffer := ByteArray new: (FFIFloat64 new typeSize).
or...
�� widthBuffer := ByteArray new: (FFIFloat64 externalTypeSize).

Now it would be nice to do...
�� widthBuffer := FFIFloat64 newBuffer.

you know, I thought the same :)
but since I��m officially on holiday I didn��t do it (yet).��

If you want to add an issue and send a PR, it would be perfect :)

https://pharo.fogbugz.com/f/cases/20699/

btw, how do we write tests for FFI?�� Do we (or can we) deliver as part of standard opensmalltalk-vm��

a small shared library "libFFITestFrame.so"��to write ffi tests against?��With functions like...

�� void passByRefOutputs(int *p_int, double *p_double) {
�� *p_int = 42;
�� *p_double = 4.2;
�� }

cheers -ben