Using a windows dll in a C++ S-function?

I have a C++ source code that is completely functional.

It uses functions from a windows DLL.

When I try to create a Simulink s-function using the legacy code tool,

these dll functions are not accessible. I get a segmentation fault.

If I take the calls to the functions out of the source code, it will run fine.

I have already changed my system path to where the dll is located. I have also checked for dependencies in the dll.

My C++ compiler is Visual Studio 2010. Matlab 32 bit 2011b

Here is how I use the legacy code tool:

clc
clear
def = legacy_code('initialize')
def.Options.language = 'C++';
def.OutputFcnSpec=['double y1 = positionfunct(void)']
def.IncPaths = {'C:\mtlb11b\bin\sfunctionblock'}
def.SrcPaths =  {'C:\mtlb11b\bin\sfunctionblock'}
def.LibPaths = {'C:\mtlb11b\bin\sfunctionblock'}
def.HeaderFiles = {'Sfile.h','windows.h'}
def.SourceFiles = {'CodeForSFile.cpp'}
def.SFunctionName = 'GetPosition'
legacy_code('sfcn_cmex_generate',def)
legacy_code('compile',def)
legacy_code('Slblock_generate',def)
legacy_code('sfcn_tlc_generate',def)
def.SampleTime = 'parameterized'

Here is how I am obtaining the functions in C++:

static HINSTANCE hGetProcIDDLL = LoadLibrary("C:/mtlb11b/bin/sfunctionblock/PCI_VME.dll");
FARPROC lpfnGetProcessID = GetProcAddress(HMODULE (hGetProcIDDLL),"OPT");
typedef int (__stdcall * pICFUNC2)(char*);
pICFUNC2 OPT; 
OPT = pICFUNC2(lpfnGetProcessID);

What are some things that I can try to get this to work? Should this work or should I be using a different approach?

[James116]

I just tried a different approach, using a c++ mex function (Although part of what I am trying to do is in Simulink, I can still do stuff in matlab). Still crashes though. So if there is advice you can give me on using dll files in either method, it would be helpful.

When I make the mex function I use the command

mex -v 'thecodefor.cpp' 'PCI_VME.lib'

to ensure that the library is linked. The library is also in the same folder as a whole bunch of dll files from some software that it originally came with, so if there is a dependency, I would think that it would solve itself.

Update: I have now also tried the loadlibrary function to put the library directly into matlab. I don't have a header though, and with the headers I am writing it doesn't work (segmentation error again).

[James116]

It is really quite frustrating. I thought that when you wrote a mex or generated a S-function, that you were just interfacing the existing C/C++ code to Matlab and that the nature of how the code was executed wouldn't change.

I'm missing something. Maybe it is simple, maybe it isn't.

[James116]

Another detail which may be of great help would be that the dll was originally compiled from Visual Basic 6.

[James116]

bump

Answer 1

[James116]

I eventually solved the problem myself. It was quite trivial. I was indexing out of an array of a return string from one of my dll functions.

Always look for the basic errors.