将VARIANT转换为...？ [英] Convert VARIANT to...?

问题描述

注意：

• 尝试调用接口的方法，返回类型为 _variant_t

代码： b
$ b

  _variant_t resultsDataString; 
 
 _bstr_t simObjectNames; 
 
 simObjectNames = SysAllocString（LTEST example 3）; 
 
 resultsDataString = pis8-> GetSimObject（simObjectNames）;包含在 .tli 中的
  

FILE：

  inline _variant_t IS8Simulation :: GetSimObject（_bstr_t Name）{
 VARIANT _result; 
 VariantInit（& _result）; 
 HRESULT _hr = get_SimObject（Name，& _result）; 
 if（FAILED（_hr））_com_issue_errorex（_hr，this，__uuidof（this））; 
 return _variant_t（_result，false）; 
} 
  

请注意：

• resultsDataString 是 struct tagVARIANT ：
  
  
  
  
  • VARTYPE vt 是9（无符号短整型）
  
  
  • IDispatch
  
  
  
  $
  b $ b
  
  
  • 我如何可以转换或提取该值？
  
  
  • VariantChangeType ？
  
  
  • 另一个方式？
  
  
  
  
  

  编辑：

  
  
  

  注意：

  
  
  
  
  

  • 希望将Visual Basic代码转换为Visual C ++

  • MFC或ATL，如果需要

  
  

  • 理想情况下，纯C ++

  
  
  
  
  

  视觉基本当量：

    example2 As SIMUL8.S8SimObject 
   Dim numberOfexamples As Variant 
   Dim resultString As Variant 
   
  设置示例1 = MySimul8.SimObject（示例1）
  设置示例2 = MySimul8。 SimObject（Example 2）
   
   numberOfexamples = example1.CountContents + example2.CountContents 
   
   resultString = CStr（numberOfexamples）& *
    

  
  

  解决方案

  COM客户端通过依靠VC ++编译器的内置COM支持。为了使客户端的编码更容易，你已经使用 #import 来生成C ++包装类，试图隐藏所有的COM细节 - 或者至少使COM细节更简单。所以你不是 直接使用COM SDK，而是使用客户端框架（我认为它像一个轻量级的COM-only框架类似于ATL或MFC）。

  
  
  

  然而，您的示例代码似乎混合了直接低级COM SDK（ VARIANT s，（ C> BSTR ， SysAllocString c> _variant_t ， _bstr_t ， XXXXPtr ）。 COM从C ++开始是复杂的 - 所以在一个完美的世界中，我建议在走得太远之前，了解COM的基本知识。

  
  
  

  但是，如果你只是想某事工作我会猜测 这是 #import -style-of-COM-clients版本的VB代码您提供：

    _variant_t example1Var; 
   _variant_t example1Var; 
   SIMUL8 :: S8SimObjectQIPtr example1; //我从VB代码猜到这个类型名称
   SIMUL8 :: S8SimObjectQIPtr example2; 
   
   example1Var = pis8-> GetSimObject（_bstr_t（LExample 1））; 
   example2Var = pis8-> GetSimObject（_bstr_t（LExample 2））; 
   if（example1Var.vt == VT_DISPATCH&& example2Var.vt == VT_DISPATCH）
   {
   // ** UPDATE **尝试勺子喂QI ptr ... 
   example1 = IDispatchPtr（（IDispatch *）example1Var）; 
   example2 = IDispatchPtr（（IDispatch *）example2Var）; 
   //这个拧紧引用计数吗？ 
   
   int numberOfexamples = example1-> CountContents + example2-> CountContents; 
   
  } 
    

  UPDATE：
  
  上的文档＃ import 这使得从C ++使用COM更容易，但还有一件事要学习...

  
  

  Note:

  • Attempting to invoke a method of an interface, of which the return type is _variant_t

  Code:

  _variant_t resultsDataString;
  
  _bstr_t simObjectNames;
  
  simObjectNames = SysAllocString (L"TEST example 3");
  
  resultsDataString = pis8->GetSimObject (simObjectNames);
  

  inline function illustrated below, contained in .tli FILE:

  inline _variant_t IS8Simulation::GetSimObject ( _bstr_t Name ) {
      VARIANT _result;
      VariantInit(&_result);
       HRESULT _hr = get_SimObject(Name, &_result);
     if (FAILED(_hr)) _com_issue_errorex(_hr, this, __uuidof(this));
      return _variant_t(_result, false);
  }
  

  Note:

  • resultsDataString is of struct tagVARIANT:
    • VARTYPE vt is 9 (unsigned short)
    • IDispatch IDispatch interface pointer

  Question

  • How can I then convert or extract the value?
  • Possible using VariantChangeType?
  • Another way?

  Edit:

  Note:

  • Looking to transform the following, Visual Basic code to Visual C++

  • MFC or ATL, if need be

  • Ideally, pure C++

  Visual basic equivalent:

  Public example1, example2 As SIMUL8.S8SimObject
  Dim numberOfexamples As Variant
  Dim resultString As Variant
  
  Set example1 = MySimul8.SimObject("Example 1")
  Set example2 = MySimul8.SimObject("Example 2")
  
  numberOfexamples = example1.CountContents + example2.CountContents
  
  resultString = CStr(numberOfexamples) & "*"
  

  解决方案

  It appears you are using C++ as a COM client by relying on the VC++ compiler's built-in COM support. To make coding the client "easier" you've used #import to generate C++ wrapper classes that attempt to hide all the COM details from you - or at least make the COM details simpler. So you're not using the COM SDK directly, but are using a client-side framework (I think of it like a light-weight COM-only framework akin to ATL or MFC).

  Your example code, however, seems to be mixing the direct low-level COM SDK (VARIANTs, BSTR, SysAllocString) with the #import COM framework (_variant_t, _bstr_t, XXXXPtr). COM from C++ is complicated at first - so in a perfect world I would suggest getting to know the basics of COM before going too far forward.

  However, if you just want something to work I would guess this is #import-style-of-COM-clients version of the VB code you provided:

  _variant_t example1Var;
  _variant_t example1Var;
  SIMUL8::S8SimObjectQIPtr example1; // I'm guessing at this type-name from the VB code
  SIMUL8::S8SimObjectQIPtr example2;
  
  example1Var = pis8->GetSimObject(_bstr_t(L"Example 1"));
  example2Var = pis8->GetSimObject(_bstr_t(L"Example 2"));
  if (example1Var.vt == VT_DISPATCH && example2Var.vt == VT_DISPATCH)
  {
     // **UPDATE** to try to spoon feed the QI ptr...
     example1 = IDispatchPtr((IDispatch*)example1Var);
     example2 = IDispatchPtr((IDispatch*)example2Var);
     // Does this screw-up reference counting?
  
     int numberOfexamples = example1->CountContents + example2->CountContents;
  
  }
  

  UPDATE:
  Documentation on #import This makes using COM from C++ much easier, but is yet one other thing to learn...

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