转自：http://blog.csdn.net/davidhsing/archive/2007/08/26/1759494.aspx
MSDN:
Difference between text mode file and binary mode file
File I/O operations take place in one of two translation modes, text or binary, depending on the mode in which the file is opened. Data files are usually processed in text mode. To control the file translation mode, you can:
a. Retain the current default setting and specify the alternative mode only when you open selected files.
b. Change the default translation mode directly by setting the global variable _fmode in your program. The initial default setting of _fmode is _O_TEXT, for text mode.
Text mode provides special processing for carriage return–linefeed pairs. When you write a newline character (0x0A) to a text-mode CStdioFile object, the byte pair (0x0D, 0x0A) is sent to the file. When you read, the byte pair (0x0A, 0x0D) is translated to a single 0x0A byte.
Note:
CStdioFile::ReadString
The CString version of this function removes the '/n' if present; the LPTSTR version does not.
说明：
这几段MSDN中的文字（来自主题：CStdioFile::ReadString）说明的问题是：
CFile类操作文件默认的是Binary模式，CStdioFile类操作文件默认的是Text模式。
在Binary模式下我们必须输入'\r\n'，才能起到回车换行的效果，'\r'只是回车（回到当前行的第一列），'\n'只是换行（到达下一行的当前列）。
而在Text模式下'\r'的工作是自动完成的，当我们写一个'\n'的时候，系统会自动帮我们在其前面加上一个'\r'，然后保存到文件里。
另外，CFile::typeText只能在CFile的子类中使用，CFile自身的Read函数不能使用CFile::typeText和CFile::typeBinary