Re: __declspec(dllexport) to return char but errors in VB6

I've found what I'm doing wrong. After reading a little feather in to StrCpy
I foud that I'm causing a buffer overrun by coping more than the origial
has. I need to test for the lenght before I copy the data.

Thanks for all your help Mattias!

Jason
Wood




"Jason W" <jason@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:OsGdUfukFHA.3936@xxxxxxxxxxxxxxxxxxxxxxx
> I didn't think I was doing it correct. I've been reading and found what I
> believe to be the correct way to do this but VB6 still errors.
>
> I can get it to work in C# but that isn't the language I'm looking for.
> Am I making since about what I'm asking for?
>
> <C# Code>
> [DllImport(@"PlotAccounting-C.dll")]
> static extern long getWdInfo(
> string param,
> System.Text.StringBuilder returnParm
> );
>
> [STAThread]
> static void Main(string[] args)
> {
> System.Text.StringBuilder returnIt = new
> System.Text.StringBuilder(500,500);
> Console.WriteLine(getWdInfo("Testing", returnIt).ToString());
> Console.WriteLine(returnIt.ToString());
> }
>
>
>
> <VB6 Code>
> Public Declare Function getWdInfo Lib "PlotAccounting-C.dll" (ByVal param
As
> String, paramOut As String) As Long
> Dim testing As String
> testing = "Not Set"
> MsgBox getWdInfo("PlotAccounting", testing)
>
> <PlotAccount-c.cpp>
> #define WIN32_LEAN_AND_MEAN
> #include <windows.h>
> #using <mscorlib.dll>
> #define WDINFO_LINKAGE __declspec(dllexport)
> #include "PlotAccounting-C.h"
> #include "shlwapi.h"
>
> __gc class ManagedObjects{
> public:
> };
>
> BOOL APIENTRY DllMain(HANDLE hModule, DWORD dwReason, LPVOID lpReserved)
> {
> return TRUE;
> }
>
> extern "C"{
> WDINFO_LINKAGE void getWdInfo(char* Param, LPTSTR returnParm){
> char __nogc* pStr =
>
static_cast<char*>(System::Runtime::InteropServices::Marshal::StringToHGloba
> lAnsi(S"Return Value").ToPointer());
> StrCpy(returnParm,pStr);
>
>
System::Runtime::InteropServices::Marshal::FreeCoTaskMem(System::IntPtr((voi
> d*)pStr));
> return;
>
> }
> }
>
>
> <PlotAccounting-c.h>
> #ifndef WDINFO_LINKAGE
> #define WDINFO_LINKAGE __declspec(dllimport)
> #endif
>
> extern "C"{
> WDINFO_LINKAGE void getWdInfo(char* Param, LPTSTR returnKey);
> }
>
>
>
>
> "Mattias Sjögren" <mattias.dont.want.spam@xxxxxxxx> wrote in message
> news:uIgQT7rkFHA.576@xxxxxxxxxxxxxxxxxxxxxxx
> > >WDINFO_LINKAGE char* getWdInfo(char* Param){
> > >
> > > IntPtr ptr = Marshal::StringToHGlobalAnsi(S"Testing return");
> > > char __nogc* pStr = static_cast<char*>(ptr.ToPointer());
> > >
> > > return pStr;
> > >
> > > Marshal::FreeHGlobal(ptr);
> > >}
> > >
> > >doesn't give me the error but doesn't return anything back.
> >
> >
> > Now the FreeHGlobal call is dead code that will never execute instead,
> > the compiler should warn you about that.
> >
> > You either have to switch to a model where the caller passes in a
> > buffer to be filled, specify that the caller must free the memory with
> > LocalFree, or provide another function that frees the memory later.
> > You can't both return the pointer and free the memory it points to in
> > the same function.
> >
> > As to why you don't get anything on the VB side, I would have to see
> > the callng code to tell.
> >
> >
> >
> > Mattias
> >
> > --
> > Mattias Sjögren [MVP] mattias @ mvps.org
> > http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
> > Please reply only to the newsgroup.
>
>


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