| Re: C++ and CALL_EXTERNAL [message #60641 is a reply to message #60627] |
Thu, 29 May 2008 04:20  |
jameskuyper
Messages: 79
Registered: October 2007
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Member |
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mark.t.douglas@gmail.com wrote:
> After an entire evening wasted trying to get IDL to interface with a
> DLL I made, I thought I'd jot down the things that I wish I had known
> at the beginning, in the hope that it will be useful to someone,
> somewhere, sometime. I was using IDL 6.1 on Windows and Microsoft's
> Visual C++ Express 2008 compiler; the same procedure will work on
> other OSes, mutatis mutadis.
>
> OK, here we go. Suppose we have two functions, written in C++, that we
> wish to use from within IDL. We naively start with the following
> header:
>
> #ifndef NORMALS_H
> #define NORMALS_H
>
> namespace Normals
> {
> __declspec(dllexport) double InverseCumulative(double x);
> __declspec(dllexport) double Cumulative(double x);
> }
>
> #endif
>
> After building the DLL and moving it to IDL's working directory, we
> type the following into IDL:
>
> x = call_external("MyLib.dll","Cumulative",double(0.5),/all_value,/
> d_value,value=[0])
>
> It can't find the function! Why? Because the polymorphism and
> overloading features of C++ are usually implemented by mangling your
> nice function names into something that looks like a core dump.
> Examine your DLL with a program like PEDUMP to figure out what
> Normals::Cumulative() is now known as; I get ?
> Cumulative@Normals@@YANN@Z . That line noise encodes precise
> information about the argument types accepted by the function, believe
> it or not. Armed with this information, we type the following into
> IDL:
>
> x = call_external("MyLib.dll","?
> Cumulative@Normals@@YANN@Z",double(0.5),/all_value,/d_value,value=[0])
Wouldn't it be simpler to disable the name mangling by declaring the
functions as 'extern "C"' ? You can still use any feature of C++ that
you want, inside the definition of the function. Of course, you can't
use any C++ features in the function interface of an 'extern "C"'
function that are not also supported by C, but CALL_EXTERNAL probably
couldn't handle those features anyway.
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