Example Using COM IDispatch Interface

com.cpp

/** Example using the COM interface without AutoCOM. The entire
 *  file can be automated with AutoCOM in under 15-lines of code.
 *
 *  #include "autocom.hpp"
 *  int main(int argc, char *argv[])
 *  {
 *      com::Bstr text;
 *      com::Dispatch dispatch("VBScript.RegExp");
 *      dispatch.put("Pattern", L"\\w+");
 *      for (auto match: dispatch.iter("Execute", L"A(b) c35 d_[x] yyy")) {
 *          match.get("Value", text);
 *          printf("Match is %S\n", text);
 *      }
 *      return 0;
 *  }
 */

#include <cassert>
#include <cstdio>
#include <dispex.h>
#include <oaidl.h>
#include <wtypes.h>


void putPattern(IDispatch *dispatch)
{
    // initialize parameters
    DISPPARAMS dp = {nullptr, nullptr, 0, 0};
    VARIANT *args = new VARIANT[1];
    DISPID named = DISPID_PROPERTYPUT;
    VariantInit(&args[0]);
    args[0].vt = VT_BSTR;
    args[0].bstrVal = SysAllocString(L"\\w+");
    dp.rgvarg = args;
    dp.cArgs = 1;
    dp.rgdispidNamedArgs = &named;
    dp.cNamedArgs = 1;

    // get function ID
    DISPID id;
    LPOLESTR string = L"Pattern";
    if (FAILED(dispatch->GetIDsOfNames(IID_NULL, &string, DISPATCH_METHOD, LOCALE_USER_DEFAULT, &id))) {
        assert(false);
    }

    // call method
    VARIANT result;
    VariantInit(&result);
    if (FAILED(dispatch->Invoke(id, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_PROPERTYPUT, &dp, &result, nullptr, nullptr))) {
        assert(false);
    }

    // cleanup
    VariantClear(&args[0]);
    VariantClear(&result);
    delete[] args;
}


IDispatch * callExecute(IDispatch *dispatch)
{
    // initialize parameters
    DISPPARAMS dp = {nullptr, nullptr, 0, 0};
    VARIANT *args = new VARIANT[1];
    VariantInit(&args[0]);
    args[0].vt = VT_BSTR;
    args[0].bstrVal = SysAllocString(L"A(b) c35 d_[x] yyy");
    dp.rgvarg = args;
    dp.cArgs = 1;

    // get function ID
    DISPID id;
    LPOLESTR string = L"Execute";
    if (FAILED(dispatch->GetIDsOfNames(IID_NULL, &string, DISPATCH_METHOD, LOCALE_USER_DEFAULT, &id))) {
        assert(false);
    }

    // call method
    VARIANT result;
    if (FAILED(dispatch->Invoke(id, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_PROPERTYGET | DISPATCH_METHOD, &dp, &result, nullptr, nullptr))) {
        assert(false);
    }

    // cleanup
    VariantClear(&args[0]);
    delete[] args;

    return result.pdispVal;
}


IEnumVARIANT * requestEnumVariant(IDispatch *dispatch)
{
    // initialize parameters
    DISPPARAMS dp = {nullptr, nullptr, 0, 0};
    VARIANT result;

    // call method
    auto hr = dispatch->Invoke(DISPID_NEWENUM, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_PROPERTYGET | DISPATCH_METHOD, &dp, &result, nullptr, nullptr);
    if (FAILED(hr)) {
        assert(false);
    }

    IEnumVARIANT *ev = nullptr;
    if (result.vt == VT_DISPATCH) {
        hr = result.pdispVal->QueryInterface(IID_IEnumVARIANT, (void**) &ev);
    } else if (result.vt == VT_UNKNOWN) {
        hr  = result.punkVal->QueryInterface(IID_IEnumVARIANT, (void**) &ev);
    } else {
        hr = E_NOINTERFACE;
    }
    VariantClear(&result);

    if (FAILED(hr)) {
        assert(false);
    }

    return ev;
}


void printMatch(IDispatch *match)
{
    // initialize parameters
    DISPPARAMS dp = {nullptr, nullptr, 0, 0};
    VARIANT result;
    VariantInit(&result);

    // get function ID
    DISPID id;
    LPOLESTR string = L"Value";
    if (FAILED(match->GetIDsOfNames(IID_NULL, &string, DISPATCH_METHOD, LOCALE_USER_DEFAULT, &id))) {
        assert(false);
    }

    // call method
    if (FAILED(match->Invoke(id, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_PROPERTYGET | DISPATCH_METHOD, &dp, &result, nullptr, nullptr))) {
        assert(false);
    }

    // get value
    printf("Match is %S\n", result.bstrVal);
    VariantClear(&result);
}


int main(int argc, char *argv[])
{
    CoInitializeEx(nullptr, COINIT_MULTITHREADED);

    // create our dispatcher
    GUID guid;
    IDispatch *dispatch;
    CLSIDFromProgID(L"VBScript.RegExp", (LPCLSID) &guid);
    if (FAILED(CoCreateInstance(guid, nullptr, CLSCTX_INPROC_SERVER, IID_IDispatch, (void **) &dispatch))) {
        assert(false);
    }

    // call methods
    putPattern(dispatch);
    auto *enumdispatcher = callExecute(dispatch);
    auto ev = requestEnumVariant(enumdispatcher);

    // iterate
    VARIANT result;
    ULONG fetched;
    if (SUCCEEDED(ev->Next(1, &result, &fetched))) {
        IDispatch *match = result.pdispVal;
        printMatch(match);
    }

    // cleanup
    ev->Release();
    enumdispatcher->Release();
    dispatch->Release();
    CoUninitialize();

    return 0;
}

The 3rd parameter of GetIDsOfNames is the number of names. This should be 1 not LOCALE_USER_DEFAULT since it has nothing to do with a localse.

@WKleinschmit you are correct about parameter #3, but the bug is, he's using DISPATCH_METHOD in that position. (LOCALE_USER_DEFAULT is in fact the symbol to use for parameter #4 unless there is some actual locale work being done.) His bug is how I ended up here in the first place, because I'm looking for a good example of Invoke(… DISPATCH_METHOD …), with little luck so far.