dll access help

hi!
I am new to c++ and for a project i have to access a dll file. And in the access details of this dll the company has given this help -

Load dll and create the main interface (ILITWriter) using the CreateWriter() export.

// CreateWriter method detail

HRESULT CreateWriter(
[out, retval] IUnknown** ppWriter
);
Parameter ppWriter - Pointer to interface pointer of new writer

Could anybody pls tell me what they are actually want to say.Specifically what doest they mean with the term - "create the main interface (ILITWriter) using the CreateWriter() export." and how should i go about this.

Thanxs,

to load a dll, you can go through your options and settings and tell your linker to link the dll file.

To use the function, try something like this

Code:

IWriter * pWriter;
CreateWriter(&pWriter);

I'm not positive that IWriter is the correct type you would want, but it looks like what they would use with the naming conventions they have.

[EDIT]
Whoops, I thought you had to create the DLL. To use the CreateWriter() functions see these pages:
http://msdn.microsoft.com/library/de...ilitwriter.asp
http://msdn.microsoft.com/library/de...ilitwriter.asp
[/EDIT]

It is expecting you to return a COM object that implements the ILITWriter interface. If you have no knowledge of COM you are going to need to start with a tutorial.

Here is the beginnings of an object that implements ILITWriter:

Code:

class CLITWriter : public ILITWriter
{
private:
  LONG m_cRefs;

public:

/* --IUnknown methods-- */
  STDMETHODIMP QueryInterface(REFIID riid, void ** ppv)
  {
  	if (ppv == NULL) return E_INVALIDARG;

  	if (IsEqualIID(riid, IID_IUnknown) || IsEqualIID(riid, IID_ILITWriter))
  	{
  		*ppv = (ILITWriter *) this;
  	}
  	else
  	{
  		*ppv = NULL;
  		return E_NOINTERFACE;
  	}

	AddRef();
	return NOERROR;
  }

  STDMETHODIMP_(ULONG) AddRef(void)
  {
  	return InterlockedIncrement(&m_cRefs);
  }

  STDMETHODIMP_(ULONG) Release(void)
  {
  	if (InterlockedDecrement(&m_cRefs) == 0)
  	{
  		delete this;
  		return 0;
  	}

  	return m_cRefs;
  }

/* --ILITWriter methods -- */

  STDMETHODIMP SetCallback(IUnknown * pCallback)
  {
    // code
  }

  STDMETHODIMP Create(const wchar_t* pwszLitFile, const wchar_t* pwszSourceBasePath,
                      const wchar_t* pwszSource, int iMinimumReaderVersion)
  {
    // code
  }

  // Rest of the ILITWriter methods
};

and here is an implementation of CreateWriter():

Code:

STDMETHODIMP CreateWriter(IUnknown** ppWriter)
{
	if (NULL == ppWriter)
	{
		return E_INVALIDARG;
	}

	CLITWriter * pLitWriter = new CLITWriter;

	*ppWriter = (IUnknown *) pLitWriter;
	
	if (NULL == *ppWriter)
	{
		return E_OUTOFMEMORY;
	}

	return NOERROR;
}

hye!
thnxs for your help. i have started learning about COM .
Could u explain what does u mean with this method of Create

STDMETHODIMP Create(const wchar_t* pwszLitFile, const wchar_t* pwszSourceBasePath,
const wchar_t* pwszSource, int iMinimumReaderVersion)
{
// code
}

i.e what code we have to written in this method.
bye!