COMをC言語から呼び出す

com.c

/* Project1.dll: http://www.asahi-net.or.jp/~kv8s-yjm/another/yja002.htm */

#define CINTERFACE

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

CLSID CLSID_Class1 =
    {0xd1890A6d,0xB213,0x11d4,{0xaf,0xc1,0x00,0xd0,0xb7,0xad,0x59,0xe8}};
IID IID_Class1 =
    {0xd1890a6c,0xb213,0x11d4,{0xaf,0xc1,0x00,0xd0,0xb7,0xad,0x59,0xe8}};

typedef struct {
    struct {
        void *QueryInterface;
        void *AddRef;
        ULONG (_stdcall *Release)(void *_this);
        void *GetTypeInfoCount;
        void *GetTypeInfo;
        void *GetIdsOfNames;
        void *Invoke;
        HRESULT (_stdcall *Add)(void *_this, int x, int y, int *ret);
    } *lpVtbl;
} IClass1;

int main(int argc, char* argv[]) {
    HMODULE hDll;
    CoInitialize(NULL);
    hDll = LoadLibraryA("Project1.dll");
    if (!hDll) printf("can not open dll\n"); else {
        HRESULT (_stdcall *DllGetClassObject)(REFCLSID, REFIID, void **) =
            (HRESULT (_stdcall *)(REFCLSID, REFIID, void**))
            GetProcAddress(hDll, "DllGetClassObject");
        if (!DllGetClassObject) printf("can not find proc\n"); else {
            HRESULT hr;
            IClassFactory *cf;
            hr = (*DllGetClassObject)(
                &CLSID_Class1, &IID_IClassFactory, (void **)&cf);
            if (FAILED(hr)) printf("ERROR: %p\n", hr); else {
                IClass1 *c1;
                hr = cf->lpVtbl->CreateInstance(
                    cf, NULL, &IID_Class1, (void **)&c1);
                if (FAILED(hr)) printf("ERROR: %p\n", hr); else {
                    int r;
                    c1->lpVtbl->Add(c1, 1, 2, &r);
                    printf("Add(1, 2) = %d\n", r);
                    c1->lpVtbl->Release(c1);
                }
                cf->lpVtbl->Release(cf);
            }
        }
        FreeLibrary(hDll);
    }
    CoUninitialize();
    return 0;
}

gistfile1.txt

Add(1, 2) = 3