.NET/Link Callback from a DLL

*To*: mathgroup at smc.vnet.net*Subject*: [mg74851] .NET/Link Callback from a DLL*From*: "Asim" <maa48 at columbia.edu>*Date*: Sun, 8 Apr 2007 05:05:48 -0400 (EDT)

Hi I am trying to use .NET/Link to call a C function (DLL) that takes a callback function pointer as an argument. I tried to follow the EnumWindows.nb example that is part of the .NET/Link documentation, but am getting an erroneous result for my function. The DLL that I am trying to call is for the C function double fpt( double (* callfunc)(double , double), double a, double b) { double c= (* callfunc)(a, b); return c; } I created a DLL for the above function using DevC++ on Windows XP, and the associated dll file is named newtry.dll. Here is what I do in Mathematica 5.2 In[2]:= Needs["NETLink`"]; In[3]:= delegateType=DefineNETDelegate["x", "double", {"double", "double"}] Out[3]= NETType[Wolfram.NETLink.DynamicDelegateNamespace.x,1] In[4]:= fpt=DefineDLLFunction["fpt", "newtry.dll", " double", {delegateType, "double", "double"}] Out[4]= Function[Null,If[NETLink`DLL`Private`checkArgCount[fpt,{##1}, 3],Wolfram`\ NETLink`DynamicDLLNamespace`DLLWrapper1`fpt[##1],$Failed],{HoldAll}] In[5]:= fptex[a_Real, b_Real]:=Module[{c}, c=a+b]; In[6]:= callbackDelegate=NETNewDelegate[delegateType, fptex] Out[6]= =ABNETObject[Wolfram.NETLink.DynamicDelegateNamespace.x]=BB In[7]:= d=fpt[callbackDelegate, 1.0, 2.0] Out[7]= 0=2E In[8]:= fptex[1.0, 2.0] Out[8]= 3=2E I As you can see, the correct answer should be 3, as in Out[8]. But the function fpt that uses the callback mechanism returns 0 as in Out 7, instead of 3. I would appreciate if someone can point out what I am doing wrong? Asim Ansari