Question

I’m trying to make a call to a method call called GetDevicesList in an interface called StillIamge and I am getting back empty results. I think it is a pointer problem but I’m not a C++ expert and I think that is the problem. The method call is:

HRESULT GetDeviceList(
  DWORD dwType,
  DWORD dwFlags,
  [out]  DWORD *pdwItemsReturned,
  [out]  LPVOID *ppBuffer
);

I know it is working as when I plug imaging devices in and out eh nubmer of returned devices goes up and down. The fact that the result is blank I think is due to me not getting the pointers correct – could someone take a quick look and let me knwo if that is the reason please?

#include "stdafx.h"

bool debug = true;

int _tmain(int argc, _TCHAR* argv[])
{
    DWORD dwStiTotal = 0;
    PSTI pSti = NULL;
    HRESULT hres = StiCreateInstance(GetModuleHandle(NULL), STI_VERSION, &pSti, NULL);

    STI_DEVICE_INFORMATION deviceInfo[255];
    memset(deviceInfo,0, sizeof(deviceInfo));

    hres = pSti->GetDeviceList(NULL, NULL, &dwStiTotal, (LPVOID*) deviceInfo); 
    printf("number devices %d\n", dwStiTotal);
    for (int i=0; i<dwStiTotal; i++){
        printf("---------------------------------------------------\n");
        printf("type %d\n", deviceInfo[i].DeviceType);
        printf("vendor %s\n", deviceInfo[i].pszVendorDescription);
        printf("device %s\n", deviceInfo[i].pszDeviceDescription);
        printf("portname %s\n", deviceInfo[i].pszPortName);
        printf("PropProvider %s\n", deviceInfo[i].pszPropProvider);
        printf("LocalName %s\n", deviceInfo[i].pszLocalName);
        printf("InternalName %s\n", deviceInfo[i].szDeviceInternalName);
    }
    pSti->Release();

    if (debug){
        char key;
        std::cin >> key;
    }

    return 0;
}

Thanks very much in advance and sorry for asking such a basic question!

Regards,

Neil

Answer 1

If you check the reference for GetDeviceList, the last parameter ppBuffer is a (pointer to a) handle to an STI-allocated buffer. You are trying to send it a buffer you allocated yourself, I believe this should even be crashing somehow…

Anyway, here is the proper way to do it

STI_DEVICE_INFORMATION* deviceInfo = NULL;
hres = pSti->GetDeviceList(NULL, NULL, &dwStiTotal, (LPVOID*) &deviceInfo);

And what we get back is a pointer to an array of STI_DEVICE_INFORMATION items, allocated by STI itself. Once you are done with it, you need to release it with LocalFree.