[fpc-pascal] windows.GetProcAddress() vs DynLibs.GetProcAddress()

[Ewald]

On 17 Jan 2014, at 21:14, Fred van Stappen wrote:

> >Ha, then you use/compiled a different version. Since a `extern "C"` preserves
> > the symbol name (that is the trick I use to link in a lot of external C++ code:
> >just put extern "C" in front of the symbol). or it could be that I am completely
> >missing something here. [for example: is the symbol `DLL_EXPORTS` defined at compile time?]
> 
> Hum, "just put extern "C" in front of the symbol" (no capito ;-( )

What I'm trying to say is that if there is `extern "C"` in front of a symbol, C++ won't mangle the name. In the cpp file you attached in one of your previous mails, [assuming a C++ compiler] this is the case as per the expansion of the  macro `SOUNDTOUCHDLL_API`; on one condition: that `DLL_EXPORTS` is defined.

[hint: read ahead to the second part first as it might just solve your problem]

Since you see mangled names, there must be an error or version mismatch somewhere in your build of the library. So I thought that perhaps you are using a compiled version of the library that still uses stdcall instead of cdecl.

To get closer to the bug, try the following:
	- Compile with debug symbols everwhere (there is no such thing as overkill ;-) )
	- Run your program in gdb and get a backtrace (`bt` on the command line of gdb), if the crash occurs at the end of the function in the library, or just after the call, then it might be a calling convention issue. If I am informed correctly (see http://stackoverflow.com/questions/3404372/stdcall-and-cdecl) then the difference between stdcall and cdecl lies in who cleans up the stack. A mismatch results in the stack being cleaned up twice or not at all. Both rather inconvenient to normal program flow. If this is the case, try changing calling conventions.


> 
> PS2 : We gonna get it, im sure...


[The Second Part -->] Well, it seems I have found something interresting here (as already suggested by Marco); you don't define THandle in your library wrapper. THandle is defined as a longint (http://www.freepascal.org/docs-html/rtl/system/thandle.html), but you need a pointer.

Try putting `Type THandle = pointer;` somewhere before the first usage of this type in your library wrapper.

--
Ewald

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