How to load & call a VBScript function from within C++?

Question

We have customers asking for VBScript functions to be called when particular actions occur within our product. I've been trying to research the Windows Scripting technologies but I'm having difficulty finding exactly what I need. Hopefully some of you can help.

Our product is a native C++ Windows product. The customer would specify a VBScript file, which we would load, and whenever a particular event occurs, we'd call a particular function in the VBScript and let it do its thing. We may provide objects within the script's namespace for it to access information about our product as well.

I found some information on MSDN about the IActiveScript interface, and some related things, but cannot find any examples of instantiating a COM object that implements this interface for VBScript.

I know that PowerShell would probably be a better option for this these days, but our customers are stuck in a lot of legacy systems and VBScript is what they know.

Any help you can provide (links or otherwise) would be appreciated!

Answer 1

I've put together a "Hello World" IActiveScript C++ ATL console application that:

• Define CSimpleScriptSite class
  • Implement IActiveScriptSite interface (mandatory)
  • Implement IActiveScriptSiteWindow interface (optional)
  • Minimum implementation with most functions implemented with a dummy stub
  • Has no error handling. Consult MSDN IActiveScriptError.
• Use CoCreateInstance a new IActiveSite object
  • Create instances of both VBScript and JScript
  • Link the IActiveSite to IActiveScriptSite using IActiveSite::SetScriptSite
  • Call QueryInterface to get an IActiveScriptParse interface
  • Use IActiveScriptParse to execute VBScript or JScript code
• The sample:
  • Evaluates an expression in JScript
  • Evaluates an expression in VBScript
  • Runs a command in VBScript

Code:

#include "stdafx.h"
#include <atlbase.h>
#include <activscp.h>

class CSimpleScriptSite :
    public IActiveScriptSite,
    public IActiveScriptSiteWindow
{
public:
    CSimpleScriptSite() : m_cRefCount(1), m_hWnd(NULL) { }

    // IUnknown

    STDMETHOD_(ULONG, AddRef)();
    STDMETHOD_(ULONG, Release)();
    STDMETHOD(QueryInterface)(REFIID riid, void **ppvObject);

    // IActiveScriptSite

    STDMETHOD(GetLCID)(LCID *plcid){ *plcid = 0; return S_OK; }
    STDMETHOD(GetItemInfo)(LPCOLESTR pstrName, DWORD dwReturnMask, IUnknown **ppiunkItem, ITypeInfo **ppti) { return TYPE_E_ELEMENTNOTFOUND; }
    STDMETHOD(GetDocVersionString)(BSTR *pbstrVersion) { *pbstrVersion = SysAllocString(L"1.0"); return S_OK; }
    STDMETHOD(OnScriptTerminate)(const VARIANT *pvarResult, const EXCEPINFO *pexcepinfo) { return S_OK; }
    STDMETHOD(OnStateChange)(SCRIPTSTATE ssScriptState) { return S_OK; }
    STDMETHOD(OnScriptError)(IActiveScriptError *pIActiveScriptError) { return S_OK; }
    STDMETHOD(OnEnterScript)(void) { return S_OK; }
    STDMETHOD(OnLeaveScript)(void) { return S_OK; }

    // IActiveScriptSiteWindow

    STDMETHOD(GetWindow)(HWND *phWnd) { *phWnd = m_hWnd; return S_OK; }
    STDMETHOD(EnableModeless)(BOOL fEnable) { return S_OK; }

    // Miscellaneous

    HRESULT SetWindow(HWND hWnd) { m_hWnd = hWnd; return S_OK; }

public:
    LONG m_cRefCount;
    HWND m_hWnd;
};

STDMETHODIMP_(ULONG) CSimpleScriptSite::AddRef()
{
    return InterlockedIncrement(&m_cRefCount);
}

STDMETHODIMP_(ULONG) CSimpleScriptSite::Release()
{
    if (!InterlockedDecrement(&m_cRefCount))
    {
        delete this;
        return 0;
    }
    return m_cRefCount;
}

STDMETHODIMP CSimpleScriptSite::QueryInterface(REFIID riid, void **ppvObject)
{
    if (riid == IID_IUnknown || riid == IID_IActiveScriptSiteWindow)
    {
        *ppvObject = (IActiveScriptSiteWindow *) this;
        AddRef();
        return NOERROR;
    }
    if (riid == IID_IActiveScriptSite)
    {
        *ppvObject = (IActiveScriptSite *) this;
        AddRef();
        return NOERROR;
    }
    return E_NOINTERFACE;
}

int _tmain(int argc, _TCHAR* argv[])
{
    HRESULT hr = S_OK;
    hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);

    // Initialize
    CSimpleScriptSite* pScriptSite = new CSimpleScriptSite();
    CComPtr<IActiveScript> spJScript;
    CComPtr<IActiveScriptParse> spJScriptParse;
    hr = spJScript.CoCreateInstance(OLESTR("JScript"));
    hr = spJScript->SetScriptSite(pScriptSite);
    hr = spJScript->QueryInterface(&spJScriptParse);
    hr = spJScriptParse->InitNew();
    CComPtr<IActiveScript> spVBScript;
    CComPtr<IActiveScriptParse> spVBScriptParse;
    hr = spVBScript.CoCreateInstance(OLESTR("VBScript"));
    hr = spVBScript->SetScriptSite(pScriptSite);
    hr = spVBScript->QueryInterface(&spVBScriptParse);
    hr = spVBScriptParse->InitNew();

    // Run some scripts
    CComVariant result;
    EXCEPINFO ei = { };
    hr = spJScriptParse->ParseScriptText(OLESTR("(new Date()).getTime()"), NULL, NULL, NULL, 0, 0, SCRIPTTEXT_ISEXPRESSION, &result, &ei);
    hr = spVBScriptParse->ParseScriptText(OLESTR("Now"), NULL, NULL, NULL, 0, 0, SCRIPTTEXT_ISEXPRESSION, &result, &ei);
    hr = spVBScriptParse->ParseScriptText(OLESTR("MsgBox \"Hello World! The current time is: \" & Now"), NULL, NULL, NULL, 0, 0, 0, &result, &ei);

    // Cleanup
    spVBScriptParse = NULL;
    spVBScript = NULL;
    spJScriptParse = NULL;
    spJScript = NULL;
    pScriptSite->Release();
    pScriptSite = NULL;

    ::CoUninitialize();
    return 0;
}

A version of the above code can be found here:

• https://github.com/stephenquan/RunScriptDemo

Answer 2

IActiveScript and related interfaces work very well. I use them in my product exactly the same way you have described. Some of out customers write their own VBScript and JScript scripts to analyze and update application data before it gets posted to a database.

You use CoCreateInstance() to instantiate IActiveScript, like you would any other COM object. You would then call its QueryInterface() method to obtain an IActiveScriptParse interface for loading snippets of scripting code, and then you update the IActiveScript's state to execute the code.

You can add custom objects to the script by implementing IDispatch-derived classes and then passing them to the engine using IActiveScript::AddNamedItem() and an IActiveScriptSite::GetItemInfo() callback.

There are examples of IActiveScript usage available on MSDN.