一个简单的问题

[yoogle]

HRESULT GetExtendedErrorInfo(BSTR *bstrErrorText);

如上，我该如何调用？

说白了，我不会使用BSTR,不知道，这个东西是不是要初始化什么的。

[yjgx007]

如果你用CString，则有一个方法AllocString将返回一个BSTR类型数据。
关于BSTR, details see MSDN

[mynamelj]

BSTR bstr;
HRESULT hr = GetExtendedErrorInfo(&bstr);
....
用完后要记得释放
SysFreeString(bstr);

[wangk]

BSTR bstrErrorText = NULL;
GetExtendedErrorInfo(&bstrErrorText);
//.....这里使用bstrErrorText。

SysFreeString(bstrErrorText);
//释放bstrErrorText，以后bstrErrorText就不可用了。

[jiaowenhao]

What Is a BSTR?
The BSTR type is actually a typedef, which in typical Windows include file fashion, is made up of more typedefs and defines. You can follow the twisted path yourself, but here's what it boils down to:

typedef wchar_t * BSTR;

Hmmm. A BSTR is actually a pointer to Unicode characters. Does that look familiar? In case you don't recognize this, let me point out a couple of similar typedefs:

typedef wchar_t * LPWSTR;
typedef char * LPSTR;

So if a BSTR is just a pointer to characters, how is it different from the null-terminated strings that C++ programmers know so well? Internally, the difference is that there's something extra at the start and end of the string. The string length is maintained in a long variable just before the start address being pointed to, and the string always has an extra null character after the last character of the string. This null isn't part of the string, and you may have additional nulls embedded in the string.

That's the technical difference. The philosophical difference is that the contents of BSTRs are sacred. You're not allowed to modify the characters except according to very strict rules that we'll get to in a minute. OLE provides functions for allocating, reallocating, and destroying BSTRs. If you own an allocated BSTR, you may modify its contents as long as you don't change its size. Because every BSTR is, among other things, a pointer to a null-terminated string, you may pass one to any string function that expects a read-only (const) C string. The rules are much tighter for passing BSTRs to functions that modify string buffers. Usually, you can only use functions that take a string buffer argument and a maximum length argument.

All the rules work on the honor system. A BSTR is a BSTR by convention. Real types can be designed to permit only legal operations. Later we'll define a C++ type called String that does its best to enforce the rules. The point is that BSTR servers are honor-bound to follow the rules so that BSTR clients can use strings without even knowing that there are rules.