_bstr_t 和CComBSTR

_bstr_t在VC中是为了兼容BSTR类型而增加的，也就是为了实现LPCSTR与BSTR转换。

它需要头文件#include <comdef.h>

_bstr_t 是BSTR的包装类
转换方法

  LPSTR   strDemo="Test";   
  _bstr_t   bstr(strDemo);  
  建议加上try，catch，用于catch(_com_error   &e)

 

The following pseudocode shows the typical use of CComBSTR:

HRESULT CMyObject::MyMethod(IOtherObject* pSomething) { CComBSTR bstrText(L"Hello"); bstrText += " again"; // LPCSTR conversion bstrText.ToUpper(); pSomething->Display(bstrText); // [in] parameter MessageBoxW(0, bstrText, L"Test", MB_OK); // Assumes Windows NT } As you can see, CComBSTR significantly simplifies the use of BSTRs. Four uses of CComBSTR, however, require special care: Freeing the BSTR explicitly Using CComBSTR as an [out] parameter Using a CComBSTR automatic variable in right-side assignments Using a CComBSTR member variable in right-side assignments 当在BSTR*所在的位置作为一个[out]参数传递CComBSTR时，你必须先调用Empty释放string的内容，就象下面这样： HRESULT CMyObject::MyMethod2(ISomething* p, /*[out]*/ BSTR* pbstr) { CComBSTR bstrText; bstrText = L"Some assignment"; // BSTR is allocated. bstrText.Empty(); // Must call empty before pSomething->GetText(&bstrText); // using as an [out] parameter. if(bstrText != L"Schaller") bstrText += "Hello"; // Convert from LPCSTR. } 因为在重写BSTR内容之前方法COM 为[out] 参数的规则是并不调用sysfreestring,这讲出现泄漏。