如何最好地将CString转换为BSTR，将其作为“in”参数放入COM方法？ [英] How to best convert CString to BSTR to pass it as an "in" parameter into a COM method?

问题描述

我需要将 CString 实例转换为正确分配的 BSTR ，并传递 BSTR 转换为COM方法。要有ANSI和Unicode编译和工作的代码，我使用 CString :: AllocSysString（）来转换任何格式 CString 到Unicode BSTR。

I need to convert a CString instance into a properly allocated BSTR and pass that BSTR into a COM method. To have code that compiles and works indentically for both ANSI and Unicode I use CString::AllocSysString() to convert whatever format CString to a Unicode BSTR.

由于没有拥有返回的BSTR，我需要处理它，并在最安全的方式调用后释放它

Since noone owns the returned BSTR I need to take care of it and release it after the call is done in the most exception-safe manner posible and with as little code as possible.

目前我使用 ATL :: CComBSTR 进行生命周期管理：

Currently I use ATL::CComBSTR for lifetime management:

 ATL::CComBSTR converted;
 converted.Attach( sourceString.AllocSysString() ); //simply attaches to BSTR, doesn't reallocate it
 interface->CallMethod( converted );

我不喜欢这里是我需要两个单独的语句来构造 ATL :: CComBSTR 绑定到转换结果。

what I don't like here is that I need two separate statements to just construct the ATL::CComBSTR bound to the convertion result.

有更好的方法来完成同样的任务吗？

Is there a better way to accomplish the same task?

推荐答案

CComBSTR 已重载 char * code>和 wchar_t * ，它们代表您调用 SysAllocString（）。所以在你的代码片段中的显式分配实际上是不必要的。以下代码也可以工作：

CComBSTR has overloaded constructors for both char* and wchar_t*, which make the call to SysAllocString() on your behalf. So the explicit allocation in your code snippet is actually unnecessary. The following would work just as well:

ATL::CComBSTR converted = sourceString;
interface->CallMethod(converted);

此外，如果您不需要使用转换的 BSTR 你的代码中的其他地方，你可以在方法调用中就地执行对象构造，像这样：

Furthermore, if you have no need to use the converted BSTR elsewhere in your code, you can perform the object construction in-place in the method call, like so:

interface->CallMethod(ATL::CComBSTR(sourceString));

同样适用于 _bstr_t 如果您不想要对ATL的依赖，可以使用 CComBSTR 代替

The same applies to the _bstr_t class, which can be used instead of CComBSTR if you don't want a dependency on the ATL.

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