Re: [Swig-user] change SWIG wrapper-function return type

[Michael R. <mic...@gm...>]

Wow.  This is hugely helpful.  David, thanks so much.

It got 99% of what I had and what it couldn't get I can do without!

msr

On Tue, Jan 25, 2011 at 9:40 AM, David Piepgrass
<dpi...@me...>wrote:

> Here’s what I (used to) use for that:
>
>
>
>
> ////////////////////////////////////////////////////////////////////////////////
>
> // Floating-point value marshalling for .NET Compact Framework:
>
> // All floating-point values must be passed by reference. MULTITHREADING
> DANGER:
>
> // For return values a pointer to a static variable is returned.
>
> %define %cs_compact_framework_float(FLOAT)
>
>                 %typemap(ctype,  out="FLOAT*") FLOAT
> "FLOAT*"
>
>                 %typemap(ctype,  out="FLOAT*") FLOAT*, FLOAT&, const FLOAT&
> "FLOAT*"
>
>                 %typemap(imtype, out="IntPtr") FLOAT, FLOAT*, FLOAT&, const
> FLOAT& "ref FLOAT"
>
>                 %typemap(cstype, out="FLOAT")  FLOAT, const FLOAT&
> "FLOAT"
>
>                 %typemap(cstype, out="FLOAT")  FLOAT*, FLOAT&        "ref
> FLOAT"
>
>                 %typemap(in)     FLOAT                               %{ $1
> = *$input; %}
>
>                 %typemap(in)     FLOAT*, FLOAT&, const FLOAT&        %{ $1
> = $input; %}
>
>                 %typemap(out, null="NULL")     FLOAT, FLOAT*, FLOAT&, const
> FLOAT& %{
>
>                                 // Not thread safe! FLOAT must be returned
> as a pointer in Compact Framework
>
>                                 static FLOAT out_temp;
>
>                                 out_temp = $1;
>
>                                 $result = &out_temp;
>
>                 %}
>
>                 %typemap(csin)   FLOAT, const FLOAT&                 "ref
> $csinput"
>
>                 %typemap(csin)   FLOAT*, FLOAT&                      "ref
> $csinput"
>
>                 %typemap(csout, excode=SWIGEXCODE) FLOAT, FLOAT*, FLOAT&,
> const FLOAT& {
>
>                                 IntPtr ptr = $imcall;$excode
>
>                                 FLOAT ret =
> (FLOAT)Marshal.PtrToStructure(ptr, typeof(FLOAT));
>
>                                 return ret;
>
>                 }
>
>                 %typemap(csvarout, excode=SWIGEXCODE2) FLOAT, FLOAT*,
> FLOAT&, const FLOAT&
>
>                 %{
>
>                                 get {
>
>                                                 IntPtr ptr =
> $imcall;$excode
>
>                                                 FLOAT ret =
> (FLOAT)Marshal.PtrToStructure(ptr, typeof(FLOAT));
>
>                                                 return ret;
>
>                                 }
>
>                 %}
>
> %enddef
>
> %cs_compact_framework_float(float)
>
> %cs_compact_framework_float(double)
>
>
>
>
>
> *From:* Michael Rosen [mailto:mic...@gm...]
> *Sent:* Monday, January 24, 2011 4:39 PM
> *To:* swi...@li...
> *Subject:* [Swig-user] change SWIG wrapper-function return type
>
>
>
> I'm using SWIG to make C# bindings that are compatible with the compact
> framework (WinCE). I've got most of the immediate issues worked through, but
> my next blocker is that some of the functions return a double. Wrappers are
> generated but they fail at run time because the CF framework will not
> marshal non-integral datatypes (
> http://msdn.microsoft.com/en-us/library/aa446536.aspx).
>
> By marshalling "double" as "double *", I can make everything work.  But how
> can i get SWIG to do this for me?
>
> An example will illustrate.  Here's the offending C++ method:
>
>
>
>
>
>    double getMaxMagnification() const
>
>    {
>
>       return m_maxMag;
>
>    }
>
> SWIG generates this wrapper:
>
>
>
>
>
> SWIGEXPORT double SWIGSTDCALL CSharp_LTIImageFilter_getMaxMagnification(void * jarg1) {
>
>   double jresult ;
>
>   LizardTech::LTIImageFilter *arg1 = (LizardTech::LTIImageFilter *) 0 ;
>
>   double result;
>
>
>
>   arg1 = (LizardTech::LTIImageFilter *)jarg1;
>
>   result = (double)((LizardTech::LTIImageFilter const *)arg1)->getMaxMagnification();
>
>   jresult = result;
>
>   return jresult;
>
> }
>
> which is NG because it marshalls a double return value.
>
> I manually changed this to return the double via a passed-in pointer:
>
>
>
>
>
> SWIGEXPORT void SWIGSTDCALL CSharp_LTIImageFilter_getMaxMagnification(void * jarg1, void *jarg2) {
>
>   fprintf(stderr, "CSharp_LTIImageFilter_getMaxMagnification\n");
>
>   //double jresult ;
>
>   LizardTech::LTIImageFilter *arg1 = (LizardTech::LTIImageFilter *) 0 ;
>
>   double result;
>
>
>
>   arg1 = (LizardTech::LTIImageFilter *)jarg1;
>
>   result = (double)((LizardTech::LTIImageFilter const *)arg1)->getMaxMagnification();
>
>   *((double*)jarg2) = result;
>
>   //jresult = result ;
>
>   //return jresult;
>
> }
>
> After making the corresponding changes (below) in the C# declaration file
> and Proxy class, this works as expected.
>
> =========================
>
> Interop Declaration
>
> NG:
>
>
>
>
>
>   [DllImport("LizardTech_SdkInterop.dll", EntryPoint="CSharp_LTIImageFilter_getMaxMagnification")]
>
>   public static extern double LTIImageFilter_getMaxMagnification(IntPtr jarg1);
>
> OK:
>
>
>
>
>
>  [DllImport("LizardTech_SdkInterop.dll", EntryPoint="CSharp_LTIImageFilter_getMaxMagnification")]
>
>   public static extern void LTIImageFilter_getMaxMagnification(IntPtr jarg1, ref double jarg2);
>
> Implementation class
>
> NG:
>
>
>
>
>
>   public override double getMaxMagnification() {
>
>     double ret = RasterSDKPINVOKE.LTIImageFilter_getMaxMagnification(swigCPtr);
>
>     return ret;
>
>   }
>
> OK:
>
>
>
>
>
> public override double getMaxMagnification() {
>
>     double ret = 0;
>
>     RasterSDKPINVOKE.LTIImageFilter_getMaxMagnification(swigCPtr, ref ret);
>
>     return ret;
>
>   }
>
> How can I get SWIG to do this for me? I think the tasks are:
>
> (a) change the return type of the wrapper function (only) from double to
> void (b) add an argument (pointer to double) to the argument list so that
> the wrapper can send back the value that way (c) make the interop
> declaration reflect the above two changes (d) make the C# wrapper invoke the
> new wrapper function.
>
> As always big-picture re-orientation is appreciated.
>