如何在纯C中使用DispCallFunc调用IStream::SetSize(0)

#include <windows.h>
#include <objbase.h>
#include <stdio.h>

typedef struct _IStreamVtbl {
    HRESULT(STDMETHODCALLTYPE *QueryInterface)(IStream *This, REFIID riid, void **ppvObject);
    ULONG(STDMETHODCALLTYPE *AddRef)(IStream *This);
    ULONG(STDMETHODCALLTYPE *Release)(IStream *This);
    HRESULT(STDMETHODCALLTYPE *Read)(IStream *This, void *pv, ULONG cb, ULONG *pcbRead);
    HRESULT(STDMETHODCALLTYPE *Write)(IStream *This, const void *pv, ULONG cb, ULONG *pcbWritten);
    HRESULT(STDMETHODCALLTYPE *Seek)(IStream *This, LARGE_INTEGER dlibMove, DWORD dwOrigin, ULARGE_INTEGER *plibNewPosition);
    HRESULT(STDMETHODCALLTYPE *SetSize)(IStream *This, ULARGE_INTEGER libNewSize);
    HRESULT(STDMETHODCALLTYPE *CopyTo)(IStream *This, IStream *pstm, ULARGE_INTEGER cb, ULARGE_INTEGER *pcbRead, ULARGE_INTEGER *pcbWritten);
    HRESULT(STDMETHODCALLTYPE *Commit)(IStream *This, DWORD grfCommitFlags);
    HRESULT(STDMETHODCALLTYPE *Revert)(IStream *This);
    HRESULT(STDMETHODCALLTYPE *LockRegion)(IStream *This, ULARGE_INTEGER libOffset, ULARGE_INTEGER cb, DWORD dwLockType);
    HRESULT(STDMETHODCALLTYPE *UnlockRegion)(IStream *This, ULARGE_INTEGER libOffset, ULARGE_INTEGER cb, DWORD dwLockType);
    HRESULT(STDMETHODCALLTYPE *Stat)(IStream *This, STATSTG *pstatstg, DWORD grfStatFlag);
    HRESULT(STDMETHODCALLTYPE *Clone)(IStream *This, IStream **ppstm);
} IStreamVtbl;

typedef struct _IStream {
    IStreamVtbl *lpVtbl;
} IStream;

typedef HRESULT(STDMETHODCALLTYPE *DispCallFunc)(void *pvInstance, ULONG oVft, CC *cc, VARTYPE vtReturn, UINT cActuals, VARTYPE *prgvt, VARIANTARG **prgpvarg, VARIANT *pvargResult);

void CallIStreamSetSize()
{
    HMODULE hOle32 = LoadLibraryA("ole32.dll");
    if (hOle32 == NULL) {
        printf("Failed to load ole32.dll\n");
        return;
    }

    DispCallFunc pDispCallFunc = (DispCallFunc)GetProcAddress(hOle32, "DispCallFunc");
    if (pDispCallFunc == NULL) {
        printf("Failed to get address of DispCallFunc\n");
        FreeLibrary(hOle32);
        return;
    }

    IStream *pStream = NULL;
    HRESULT hr = CoCreateInstance(&CLSID_NULL, NULL, CLSCTX_INPROC_SERVER, &IID_IStream, (void **)&pStream);
    if (FAILED(hr)) {
        printf("Failed to create IStream instance\n");
        FreeLibrary(hOle32);
        return;
    }

    IStreamVtbl *pStreamVtbl = pStream->lpVtbl;
    ULONG oVft = (ULONG)((char *)&pStreamVtbl->SetSize - (char *)pStreamVtbl);
    CC cc = CC_STDCALL;
    VARTYPE vtReturn = VT_HRESULT;
    UINT cActuals = 2;
    VARTYPE rgvt[2] = { VT_UNKNOWN, VT_UI8 };
    VARIANTARG pvarg[2] = { 0 };
    pvarg[0].vt = VT_UNKNOWN;
    pvarg[0].punkVal = NULL;
    pvarg[1].vt = VT_UI8;
    pvarg[1].ullVal = 0;

    VARIANT vResult;
    VariantInit(&vResult);

    hr = pDispCallFunc(pStream, oVft, &cc, vtReturn, cActuals, rgvt, &pvarg, &vResult);
    if (FAILED(hr)) {
        printf("Failed to call IStream::SetSize\n");
    } else {
        printf("IStream::SetSize called successfully\n");
    }

    VariantClear(&vResult);
    pStream->lpVtbl->Release(pStream);
    FreeLibrary(hOle32);
}

int main()
{
    CoInitialize(NULL);
    CallIStreamSetSize();
    CoUninitialize();
    return 0;
}