BSTR与wchar_t*的真正区别

[spdia]

typedef /* [wire_marshal] */ OLECHAR __RPC_FAR *BSTR; in wtypes.h
typedef WCHAR OLECHAR; in wtypes.h
typedef wchar_t WCHAR; in winnt.h
typedef unsigned short wchar_t; in ctype.h


wchar_t wstrsource[16]=L"hello world";
BSTR bstrhello=::SysAllocString(wstrsource);
cout<<::SysStringLen(bstrhello)<<"\n";
cout<<::SysStringLen(wstrsource)<<"\n";

RESULT
11
2720172

wchar_t wstrsource[16]=L"hello\0world";
BSTR bstrhello=::SysAllocString(wstrsource);
cout<<::SysStringLen(bstrhello)<<"\n";
cout<<::SysStringLen(wstrsource)<<"\n";

RESULT
5
2720172

Q1:为什么会出现这样的结果?SysAllocString怎么判断字符串结束?'\0'会在"hello world"后自动添加?
Q2:BSTR与wchar_t *的区别?
Q3:wchar_t wstrsource[16]=L"hello\0world";中L的作用?

[随风bj]

1.一般以'\0'判断字符串结束（也就是NULL）,在初始化字符串时每个空的位置都是0
2.
3.将字符串转换为通用的ascii码值

[rockswang]

下面是直接从MSDN里copy来的，注意最后一句。

SysAllocStringLen
BSTR SysAllocStringLen(
OLECHAR FAR* pch,
unsigned int cch
);

Allocates a new string, copies cch characters from the passed string into it, and then appends a null character.

Note: This function does NOT convert a char * string into a unicode BSTR. The BSTR returned with this function can only be used with 16 bit applications.

Parameters
pch
A pointer to cch characters to copy, or Null to keep the string uninitialized.
cch
Number of characters to copy from pch. A null character is placed afterwards, allocating a total of cch+1 characters.

[Fesd]

Q1: 根据'\0'判断字符串结束
Q2: wchar_t* 只是一个简单的指针 跟int* ,char* 一样
BSTR 所指向的内存地址相当于一个wchar_t*,但BSTR往后退4Bytes（在内存中）的
地址中所存的一个DWORD值表示它的长度。

例如：
BSTR bstrT = ::SysAllocString(L"....");//（内存地址）0x00001000;
LPDWORD lpdwLen = (LPBYTE)bstrT - 4; //(相当于0x0000FFC)
ASSERT(*lpdwLen == ::SysStringLen(bstrT);

注意:SysStringLen的参数类型是BSTR而非wchar_t*

Q3: L""告诉编译器把双引号中的字符串按双字节（wchat_t）处理

[spdia]

原来如此,我明白了.谢谢各位!!!!