bstr_t在VC中是為了兼容BSTR類(lèi)型而增加的，也就是為了實(shí)現(xiàn)LPCSTR與BSTR轉(zhuǎn)換。
它需要頭文件#include
bstr_t 是BSTR的包裝類(lèi)
轉(zhuǎn)換方法
LPSTR strDemo="Test";
bstr_t bstr(strDemo);
建議加上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
當(dāng)在BSTR*所在的位置作為一個(gè)[out]參數(shù)傳遞CComBSTR時(shí)，你必須先調(diào)用Empty釋放string的內(nèi)容，就象下面這樣：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?yàn)樵谥貙?xiě)B(tài)STR內(nèi)容之前方法COM 為[out] 參數(shù)的規(guī)則是并不調(diào)用sysfreestring。
它需要頭文件#include
bstr_t 是BSTR的包裝類(lèi)
轉(zhuǎn)換方法
LPSTR strDemo="Test";
bstr_t bstr(strDemo);
建議加上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
當(dāng)在BSTR*所在的位置作為一個(gè)[out]參數(shù)傳遞CComBSTR時(shí)，你必須先調(diào)用Empty釋放string的內(nèi)容，就象下面這樣：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?yàn)樵谥貙?xiě)B(tài)STR內(nèi)容之前方法COM 為[out] 參數(shù)的規(guī)則是并不調(diào)用sysfreestring。