CString is based on the TCHAR data type. If the symbol _UNICODE is defined for your program, TCHAR is defined as type wchar_t, a 16-bit character type; otherwise, it is defined as char, the normal 8-bit character type. Under Unicode, then, CString objects are composed of 16-bit characters. Without Unicode, they are composed of 8-bit char type.
When not using _UNICODE, CString is enabled for multibyte character sets (MBCS, also known as double-byte character sets, DBCS). Note that for MBCS strings, CString still counts, returns, and manipulates strings based on 8-bit characters, and your application must interpret MBCS lead and trail bytes itself.
CString objects also have the following characteristics:
(1)CString objects can grow as a result of concatenation(串联) operations.
(2)CString objects follow “value semantics.” Think of a CString object as an actual string, not as a pointer to a string.
(3)You can freely substitute(替换) CString objects for const char* and LPCTSTR function arguments.
(4)A conversion operator gives direct access to the string’s characters as a read-only array of characters (a C-style string).
Tip Where possible, allocate CString objects on the frame rather than on the heap. This saves memory and simplifies parameter passing.
CString assists you in conserving memory space by allowing two strings sharing the same value also to share the same buffer space. However, if you attempt to change the contents of the buffer directly (not using MFC), you can alter both strings unintentionally. CString provides two member functions, CString::LockBuffer and CString::UnlockBuffer, to help you protect your data. When you call LockBuffer, you create a copy of a string, then set the reference count to -1, which "locks" the buffer. While the buffer is locked, no other string can reference the data in that string, and the locked string will not reference another string. By locking the string in the buffer, you ensure that the string’s exclusive hold on the data will remain intact. When you have finished with the data, call UnlockBuffer to reset the reference count to 1.
详细介绍见MSDN。。。。。 呵呵。
C++自己实现的CString类：