C ++ Primer: Chapter 8 summary

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Chapter 8: IO Libraries

8.1 IO class

IO libraries and header files types

head File	Types of
iostream	istream, wistream data stream read from ostream, wostream data is written to the stream iostream, wiostream stream read
fstream	ifstream, wifstream data read from a file ofstream, wofstream data is written to the file fstream, wfstream read and write files
sstream	istringstream, wistringstream data string read from ostringstream, wostringstream data is written to the string the stringstream, write string wstringstream

1. iostream defines the basic types stream for reading and writing; the fstream defines the type of read and write file name; sstream defines the type of read-write memory string object.
2. and istringstream ifstream inherits from istream, ofstream and ostringstream inherited from ostream.

IO object can not copy assignment

1. Since the object can not be copied and assigned IO, parameters, or it can not be a type of return flow type. IO operations function normally passed by reference and return flow.
2. A write IO object changes its state, it is not transmitted, and the returned reference is const.

Condition Status

Condition Status	description
:: steep iostate	IO is strm type iostate is related to a type of machine, there is provided a fully functional state condition expression
:: steep badbit	It used to indicate flow has crashed
:: steep failbit	It used to indicate that an IO operation has failed
:: steep eofbit	Used to indicate the flow reaches the end of the file
:: steep goodbit	Used to indicate the flow is not in an error state. This value is zero guarantee
s.eof()	If the set flow eofbit s Returns true
s.fail()	If the set flow badbit or failbit s Returns true
s.bad()	If the set flow badbit s Returns true
s.good()	If the stream is active s, return true
s.clear()	S for all the flow condition state bit is reset, the state is set to a valid flow. Return void
s.clear(flags)	flags strm :: iostate type is according to the given flag bit flags, the flow condition state s corresponding bit is reset. Return void
s.setstate(flags)	flags strm :: iostate type is according to the given flag bit flags, the flow condition corresponding status bit s. Return void
s.rdsate ()	Returns the current state of the stream s condition, the return type is strm :: iostate

1. Before using a stream, it must first check whether the flow is in good condition.

while(cin>>word)
    // ok：读操作成功....

2. badbit a system-level error such as an unrecoverable read error, can not be reused in the event stream; represents the failbit recoverable error, as desired read data is inconsistent with the actual read data type, can be corrected after the occurrence of flow can still be used; if reaches the end of file position, and the failbit eofbit will be set; goodbit value of 0, a flow error did not occur.
3. Good () Returns all error bits in the case where no set true; Returns true bad (), fail (), eof () at the position corresponding to the error bit is asserted; badbit when the position is, fail () Returns ture. Therefore, use Good () or fail () determine the overall state of the stream.

Output Buffer Management

1. Data output stream may be output immediately, and might temporarily stored in the buffer to re-output.
2. Flushes of reasons: the program ends normally, as part of the main function of the return operation, the refresh buffer; buffer is full, the subsequent data must first refresh buffer to the write buffer; endl The manipulator using the explicit refreshing buffer; using unitbuf to set the internal state of the stream buffer is empty, is set for unitbuf cerr, refresh may be implemented immediately cerr; output stream cin, cerr cout is associated to another stream, read or write cin cout cerr cause refresh buffer.
3. Wrap endl and flush the buffer; flush only refresh buffer; ends first insert a blank character and then flushes the buffer.
4. unitbuf flush after each output operation is achieved by the buffer is flushed; nounitbuf to reset the stream, so that the buffer or normal mode.
5. If the program crashes, the output buffer is not refreshed its data output may remain in the buffer waiting to be printed.
6. tie no arguments returns a pointer to the output stream; ostream accepts a pointer to associate themselves to this tie ostream.

8.2 File Input Output

fstream specific operation

operating	description
fstream fstrm;	fstream fstream header file is a type defined to create an unbound stream file
fstream fstrm(s);	s is a pointer to a string type or C-style string to create a fstream, and open the file named s of this constructor is explicit
fstream fstrm(s, mode);	mode included in, out, app, ate, trunc, binary create a fstream, open the file named s specified mode of this constructor is explicit
fstrm.open(s);	Open the file named s, and will file with the fstrm binding, return void
fstrm.close();	The file is closed and fstrm bound to return void
fstrm.is_open();	Determine whether the file is opened with fstrm bound to succeed, and has not been closed, return bool

1. 头文件fstream定义3个类型来支持文件IO：ifstream从一个给定文件读取数据；ofstream向一个给定文件写入数据；fstream可以读写给定文件。

使用文件流对象

1. C++11标准中，文件名可以是库类型string对象，也可以是C风格字符数组。旧版本只允许C风格字符数组。
2. 调用open()失败时，failbit被置位。故最好检测open()是否打开成功。

if(out)
    //检测成功后，再使用out

3. 若文件流已打开过文件，它调用open()会失败，并使failbit被置位。若文件流想打开其它文件，必须先关闭再打开。
4. 当一个fstream对象离开其作用域时，与之关联的文件会自动关闭。

文件模式

文件模式	描述	前置要求	适合对象
in	以读方式打开	无	ifstream、fstream
out	以写方式打开	默认trunc	ofstream、fstream
app	文件末尾进行写操作	默认out，无trunc	ofstream、fstream
trunc	截断文件，清空文件后再进行写操作	有out	ofstream、fstream
ate	打开文件后立即定位到文件末尾	无	任何对象
binary	以二进制方式进行IO	无	任何对象

1. 单独以out模式打开文件，会默认使用trunc模式，删除旧内容。
2. 以out+app模式或者out+in模式打开文件，可保留文件旧内容。
3. ifstream默认以in模式打开；ofstream默认以out模式打开； fstream默认以in+out模式打开。

8.3 string流

stringstream特有操作

操作	描述
sstream strm;	sstream是头文件sstream中定义的一个类型 strm是一个未绑定的stringstream对象
sstream strm(s);	strm是一个sstream对象，保存string s的一个拷贝。 此构造函数是explicit。
strm.str();	返回strm所保存的string的拷贝
strm.str(s);	将string s拷贝到strm中，返回void

1. sstream头文件定义3个类型来支持IO：istringtream从string读取数据；ostringtream向string写入数据；stringstream对string读写数据。
2. 整行文本处理时，可用istringtream处理行内单词；逐步构造，同一打印输出时使用ostringtream。