CString's GetBuffer & ReleaseBuffer

Modifying CString Contents Directly

In most situations, you should use CString member functions to modify the contents of a CString object or to convert the CString to a C-style character string.

However, there are certain situations, such as working with operating-system functions that require a character buffer, where it is advantageous to directly modify the CString contents.

The GetBuffer and ReleaseBuffer member functions allow you to gain access to the internal character buffer of a CString object and modify it directly. The following steps show how to use these functions for this purpose:

1. Call GetBuffer for a CString object and specify the length of the buffer you require.

2. Use the pointer returned by GetBuffer to write characters directly into the CString object.

3. Call ReleaseBuffer for the CString object to update all the internal CString state information, such as the length of the string. After modifying a CString object's contents directly, you must call ReleaseBuffer before calling any other CString member functions.

再给出一些CString和BSTR的转换：

CString 型转化成 BSTR 型

当我们使用 ActiveX 控件编程时，经常需要用到将某个值表示成 BSTR 类型.BSTR 是一种记数字符串，Intel平台上的宽字符串（Unicode），并且可以包含嵌入的 NULL 字符。

可以调用 CString 对象的 AllocSysString 方法将 CString 转化成 BSTR：

CString str;

str = .....; // whatever

BSTR bStr = str.AllocSysString();

 

BSTR型转换为CString

如果你在 UNICODE 模式下编译代码，你可以简单地写成：

CString convert(BSTR bStr)

{

    if(bStr == NULL)

        return CString(_T(""));

    CString s(bStr); // in UNICODE mode

    return s;

}

如果是 ANSI 模式

CString convert(BSTR b)

{

    CString s;

    if(b == NULL)

       return s; // empty for NULL BSTR

#ifdef UNICODE

    s = b;

#else

    LPSTR p = s.GetBuffer(SysStringLen(b) + 1);

    ::WideCharToMultiByte(CP_ACP,            // ANSI Code Page

                          0,                 // no flags

                          b,                 // source widechar string

                          -1,                // assume NUL-terminated

                          p,                 // target buffer

                          SysStringLen(b)+1, // target buffer length

                          NULL,              // use system default char

                          NULL);             // don''t care if default used

    s.ReleaseBuffer();

#endif

    return s;

}