overview

provide a unified interface for interacting with external input

stream:a character buffer automatically interacts with the external source

把变量转换成字符串的形式 （可以写入buffer）

stringstream

not connected to any external source creat extract insert

• constructors istringstream iss("initial"); osstringstream oss("initial");

  //can provide "modes"such as ate(start at end位置 )or bin(read as binary) isstringstream iss("initial",stringstream::bin); ostringstream oss("initial",osstringstream::ate)

key takeaways

• 做什么？ >>extracts the next variable of a certain type,up to the next whitespace

• 为什么>>和<<可以chain 起来？ the >>and<< operators return a reference to the stream itself,so in each instance the stream is the left hand operand
• 有没有一个stringstream可以读和写 有，reading and writing 同时但 can often lead to subtle bugs

input streams

从目标源或外部员读取数据的一种方法

std::cin是console input stream

• std::cin is buffered
• 是一个用户可以存 取数据的一个地方
• std::nufferstops at a whitespace
• whitespace in c++ includes:
• " "
• \n
• \t

statebits

四种

• good bit:ready for read/write; nothing unusual,on when other bits areoff
• fail bit: previous operation failed, all future operations frozen type mismatch,file cannot beopened,seekg failed
• eof bit: previous operation reached the end of buffer content reach ed the end of the buffer
• bad bit:external error,likely irrecoverable could not move characters to buffer from external source(正在读取的文件突然被删除了)

main takeaways

• streams are a general interface to read and write data in programs
• input and output streams on the same source/destination type compliment each other
• 不要将getline()和std::cin()一起使用，一般情况下,getline()会读入空格
• std::cin() - leaves the newline in the buffer
• getline() - gets rid of the newline