BSTR详解五 - BSTR与其它字符串类型转换

逍遥公子

1、类型转换

常用字符串件的类型转换。

From	To	Sample
字符串常量	BSTR	Right: BSTR bs = ::SysAllocString(_T("Test string")); … ::SysFreeString(); Wrong: BSTR bs = _T("Test string"); //ERROR
LPWSTR / LPCWSTR / WCHAR* / wchar_t	BSTR	Right: LPCTSTR sz1 = _T("Test String"); BSTR bs = ::SysAllocString(sz1); … ::SysFreeString(); Wrong: LPTSTR sz1 = _T("Test String"); BSTR bs = sz1; //ERROR
BSTR	LPCWSTR / const WCHAR * / const wchar_t *	Right: BSTR bs = ...; // ... LPCTSTR sz = static_cast<LPCTSTR>bs; ... ::SysFreeString(bs); //Never use sz after this line Wrong: BSTR bs = ...; // ... LPCTSTR sz = bs; ... ::SysFreeString(bs); //Never use sz after this line _tcslen(sz); //ERROR
BSTR	LPWSTR / WCHAR* / wchar_t*	Right: BSTR bs = ...; // //... UINT len = ::SysStringLen(bs); // Do not modify the BSTR content by // C/C++ string functions LPTSTR sz = new TCHAR[len+1]; _tcsncpy(sz, bs, len); ::SysFreeString(bs); delete []sz; Wrong: BSTR bs = ...; // //... // Do not modify the BSTR content by // C/C++ string functions LPTSTR sz = bs; //Error
CString	BSTR	Right: CString str1 = ...; BSTR bs = str1.AllocSysString(); SomeMethod(bs); // void SomeMethod([in]BSTR) ::SysFreeString(bs); CComBSTR bs1(static_cast<LPCTSTR>(str1)); SomeMethod(static_cast<BSTR> (bs1) ); // void SomeMethod([in] BSTR ) _bstr_t bs2( static_cast<LPCTSTR>(str1)); SomeMethod(static_cast<BSTR> (bs2) ); Wrong: CString str1 = ...; SomeMethod(str1.AllocSysString()); // No one will releasee the return BSTR of // str1.AllocSysString()
BSTR	CString	Right: BSTR bs = SysAllocString(_T(“Test”)); CString str1(bs); CString str2; Str2 = bs; SysFreeString(bs); // Never forget this line
char* / LPSTR / LPCSTR	BSTR	Right: Solution 1： char str[MAX_STR_LEN] = "ANSI string"; WCHAR wstr[MAX_WSTR_LEN]; // Convert ANSI to Unicode MultiByteToWideChar( CP_ACP, 0, str,         strlen(str)+1, wstr,        sizeof(wstr)/sizeof(wstr[0]) ); BSTR bs1 = ::SysAllocString(wstr); CString cs = str; BSTR bs2 = cs.AllocSysString() Solution 2： char str[MAX_STR_LEN] = "ANSI string"; _bstr_t bs1(str); CComBSTR bs2(str); Wrong: char *str = "ANSI string"; BSTR bstr1 = SysAllocString(             (const OLECHAR*) str);
BSTR	char* / LPSTR / LPCSTR	Right: Solution 1： char str[MAX_STR_LEN]; BSTR bs = ::SysAllocString(L"Test"); // Convert ANSI to Unicode WideCharToMultiByte( CP_ACP, 0,    (LPCWSTR)bs, -1,    str, MAX_STR_LEN, NULL, NULL ); ::SysFreeString(bs); Solution 2： BSTR bs = ::SysAllocString(L"Test"); _bstr_t bs1(bs, false); const char* str = static_cast <const char*> bs1; Wrong: BSTR bstr1 = SysAllocString(L”ANSI string"); char *str = (char*) bstr1;

IMPORTANT: 上面所有的例子都是按照UNICODE应用程序设计的。并且不考虑BSTR中包含多个字串的情况，也就是BSTR只在结束的位置有一个0结束符。对于MBCS/ANSI程序，可以参考上面的例子。主要区别是对于现在的COM版本OLECHAR是wchar_t，但是TCHAR 对于UNICODE程序才是wchar_t。