C++ CLI cryptic function call

Question

So I'm trying to call a function that is a manged wrapper around an OCX object. Having great difficulty. Function is;

foo(System::Object ^% theBuffer)

where 'theBuffer' is an array of bytes. The template for the unmanaged OCX which 'foo' wraps is

goo(VARIANT* theBuffer);

So I've tried;

System::Int32 buf[10];
foo(buf);

which fails. And

Bitmap ^b;
foo(b);

which compiles but obviously the called function is not going to create a .NET bitmap for me.

So I guess the question is how do I pass this function a block of memory it can write to and then get access to it back in .NET world.

Thanks

Answer 1

You can't convert a VARIANT to the buffer directly.

First you need to check what kind of object is stored in it by checking theBuffer->vt. The returned value will be of the type VARTYPE .

Answer 2

What about something like..

Bitmap ^b = gcnew Bitmap(...
foo(b);

Answer 3

ok so I'm actually using the Axis Media Control SDK to interface with a network camera ( http://www.axis.com/techsup/cam_servers/dev/activex.htm ). The OCX function I am calling via the wrapper looks like;

HRESULT GetCurrentImage(int theFormat,    [C++]
        VARIANT* theBuffer,
        LONG* theBufferSize
       );

the wrapper is supplied by Axis. Using .NET Reflector I have disasembled the wrapper function;

public: virtual void __gc* GetCurrentImage(Int32 __gc* theFormat, [Out] Object __gc*   *theBuffer, [Out] Int32 __gc* *theBufferSize)
{
    if (this->ocx == 0)
    {
        throw __gc new InvalidActiveXStateException(S"GetCurrentImage", ActiveXInvokeKind::MethodInvoke);
    }
    this->ocx->GetCurrentImage(theFormat, out theBuffer, out theBufferSize);
}

So it's not doing anything smart, just passing a chunk of memory. In C++ CLI syntax the template looks like;

GetCurrentImage(int theFormat, System::Object ^% theBuffer, int % theBufferSize)

So my question becomes how do I pass this a chunk of memory to write to and then recover it back into a .NET object. I tried this;

unsigned char c[100];
GetCurrentImage(0, (System::Object)c, BufSize);

but obviously it dosn't work.

Answer 4

I've just tried;

unsigned char a[1024*256];
System::IntPtr^ iPtr = gcnew System::IntPtr(a);
myAMC->GetCurrentImage(0, iPtr, BufferSize);

which compiles but dosn't write the buffer to 'a' .

Answer 5

//compile with /CLR (VS2005:sp1, vs2008)

class A {

public:

A(char *c)
{
 printf("this %x\n",this);
 strcpy(m_c,c);
}

char m_c[4096];   //use high memory >=4096

~A(){}      //to reproduce this bug

};

class B {

public:

B(char *c)
{
 printf("this %x\n",this);
 strcpy(m_c,c);
}

char m_c[4096];

};

void func(A a="2",B b="1") { printf("%s:%x %s:%x\n",a.m_c, &a, b.m_c, &b); }

int _tmain(int argc, TCHAR argv[]) { func(); return 0; }

//prints garbage value, want to know if this is a bug in the compiler