COM returns array of bytes

Hi everybody:)

I have a com object that returns an array of bytes:

Code:

---

public Byte[] ReadCodePage(bool IsCode, UInt32 Address, Int32 NumberOfBytes)

---

From the client, I have VS 2003. How do I call this function. I am aware of SAFEARRAY, and CComSafeArray, but I am having no success using it.
Can somebody send me a short post on how to do this, and access the bytes after the function call? All help is much appreciated.

-rlien

If you are trying to call something via a COM interface, you would probably want an HRESULT as the return value and pass a byte array pointer to the function all. I am not clear on all the details, but a basic COM call might look something like this:

Code:

---

(server)

STDMETHODIMP AddTwoNumbers(int x, int y, int *result)
{
  result = x + y;
  return S_OK;
}

---

Code:

---

(client)

int x = 2;
int y = 3;
int result = 0;
HRESULT hr = AddTwoNumbers(x, y, &result);

---

If you want to get into safe arrays, I can show examples on that, but I think you need to adjust your call to COM first (unless I am missunderstanding the question).

I failed to mention that this component is written in C#, 2005 express.

I'm confused - did you create a dll in C# that you hope to include in your client and make calls to it? If so, then you just need to reference it within your project.

Or

Do you have a C++ dll that you want to use C# to make a call to?

In either case you need to make a reference to the COM object in the C# project.

The dll is written in c#, 2005 express edition.
My client is written in vc++, visuall studio 2003.

I my client header I have

Code:

---

#import ".\Mydll.tlb" raw_interfaces_only

---

My initiall assumption was that I make the call

Code:

---

SAFEARRAY SA;
.
.
.
spSomeSmartPointer->ReadCodePage(bvarIsCodePage, nAddress, nBytesToRead, &SA);

---

Furthermore, my problem as I see it is to set up the safearray, and then access the byte array that the dll returned.

So what you are saying is that you have a managed dll (C#) which is being called by unmanaged C++. I believe this will help you:

Code:

---

// Managed Code (C#) includes
#pragma warning (disable: 4278)
#import <mscorlib.tlb> raw_interfaces_only

#if defined (USINGPROJECTSYSTEM)
#import ".\Mydll.tlb" no_namespace named_guids
#else
#import ".\Mydll.tlb" no_namespace named_guids
#endif

// Project settings for using managed and unmanaged code
//1) Go To ---Project Property->Configuration Property --->c/c++ --->/clr
//2) Go To ---Project Property->Configuration Property --->Code Generation-->Basic Runtime Checks-->Default
//3) Go To ---Project Property->Configuration Property --->Code Generation-->Enable Minimal Rebuild--> N
//4) Go To ---Project Property->Configuration Property --->c/c++ -->General-->Debug Information Format-->Program Database (/Zi)
//5) Go To ---Project Property->Configuration Property --->Code Generation-->Runtime Library--><inherit from project defaults>

---

Now, to look at your function call:

public Byte[] ReadCodePage(bool IsCode, UInt32 Address, Int32 NumberOfBytes)

I think this will return as a VARIANT, which is a type of SafeArray. You can actually use the call SafeArrayGetElement(array.parray, &index, &item) with index being a long and item being a BSTR (or whatever you are getting back).

Hi drm,

I do know it returns a safearray. My initial problem was how to use this safe array.

Code:

---

SAFEARRAY *pSA;
SAFEARRAYBOUND aDim[1];    // one dimensional array
aDim[0].lLbound= 0;
aDim[0].cElements= 32;
char * pActualData= NULL;

pSA= SafeArrayCreate(VT_UI1,1,aDim);

spIOCDTPtr->ReadCodePage(bvarIsCodePage, nAddress, nBytesToRead, &pSA);

---

My initial intension has been something along the lines as above. Due to my limited knowledge on safearrays I am not able to set it up correctly or retrieve the bytes from it after the call.

roar

To create the SafeArray you can do the following:

Code:

---

// Create the SAFEARRAY
USES_CONVERSION;
SAFEARRAY *pSA;
SAFEARRAYBOUND dimensions[1];
dimensions[0].lLbound = 0;
dimensions[0].cElements = numItemNames;
pSA = SafeArrayCreate(VT_VARIANT, 1, dimensions);
if (pSA == NULL)
{
        return E_FAIL; // unable to create the safearray
}

---

To insert items into a SafeArray you can use the following:

Code:

---

long index = 0;
string itemName = "foo";

_variant_t itemNameVariant;
itemNameVariant = A2W(itemName.c_str());
HRESULT hr = SafeArrayPutElement(pSA, &index, &itemNameVariant);
if (FAILED(hr))
{
        SafeArrayDestroy(pSA);
        return E_FAIL;
}

---

To get items out of the SafeArray you would do the following:

Code:

---

BSTR item = NULL;
long index = 0;
SafeArrayGetElement(pSA.parray, &index, &item);

---

I think how you are calling it is incorrect, but I don't know the code. You might want to try this instead:

Code:

---

int nBytesToRead= 0;
int index = 0;
BSTR item = NULL;

VARIANT foo = spIOCDTPtr->ReadCodePage(bvarIsCodePage, nAddress, nBytesToRead);

SafeArrayGetElement(foo.parray, &index, &item);

---

By doing the above, you are stating that an object is being returned and within that object you want to access the array within it. You can write a loop around SafeArrayGetElement which will be the value of your index.

Jepp drm,
You nailed it. If any is facing the same issue here it is:

Code:

---

// read a page
    INT32 nBytesToRead = 4;

    // Create the SAFEARRAY
    USES_CONVERSION;
    SAFEARRAY *pSA;
    SAFEARRAYBOUND dimensions[1];
    dimensions[0].lLbound = 0;
    dimensions[0].cElements = nBytesToRead;
    pSA = SafeArrayCreate(VT_VARIANT, 1, dimensions);
    if (pSA == NULL)
    {
            return 0; // unable to create the safearray
    }

    VARIANT_BOOL bvarIsCodePage = true;
    INT32 nAddress = 0;
 
    pIOCDLPPtr->ReadCodePage(bvarIsCodePage, nAddress, nBytesToRead, &pSA);

    BYTE item = 0;

    for(long i = 0; i < nBytesToRead; i++)
        SafeArrayGetElement(pSA, &i, &item);

---

and the c# dll

Code:

---

public Byte [] ReadCodePage(bool IsCode, UInt32 Address, Int32 NumberOfBytes)
{

            Byte[] bTest= new Byte[4];

            bTest[0] = 0x55;
            bTest[1] = 0x56;
            bTest[2] = 0x57;
            bTest[3] = 0x58;

            return bTest;
}

---

Go Cylones (and Vikings)! Happy friday:)

roar