lec1 Streams

streams

overview

• interact with some devices
  • console & keyboard
  • files
  • pipelines
  • sockets
• stream is a unified interface.
  • in all devices do the same thing
  • for many interactions, stream provide a unified interface
• two challenge
  • we need to retrieve/send data from the source in string form
  • we need to convert between data in our program and its string representation
• streams provide a unified interface for interacting with external iput
  • just imagine a stream to be a character buffer that automatically interacts with the external source
  • streams also convert variables to a string form that can be written in the buffer
  • we use » & « to interacts with streams interface
• 我们只需要关注如何使用»和«，想象streams是一个buffer即可，别的无需考虑

string stream

• output stream
  • each streams has it’s own buffer
  • why streams instead of characters buffer?
    • streams can read a integer from it’s buffer, character buffer cann’t do it

    #include <iostream>
    #include <sstream>
  
    int main () {
        std::ostringstream oss("Ito-En Green Tea", std::stringstream::ate);
        std::cout << oss.str() << std::endl;
        oss << "16.9 Ounces";
        std::cout << oss.str() << std::endl;
        return 0;
    }
  

  • if we don’t use std::stringstream::ate, output will be 16.9 Ouncesn Tea.

  • oss << 16.9 << " Ounces; means number 16.9 will convert to chars(‘1’, ‘6’, ‘.’, ‘9’ and so on) in the buffer intead of double number

• input stream

    #include <iostream>
    #include <sstream>
    int main () {
        std::istringstream iss("16.9 Ounce");
        double amount;
        std::string unit;
        iss >> amount;
        amount /= 2;
        iss >> unit;
        std::cout << "amount: " << amount << " unit: " << unit << "\n";
    }
  

  • input stream 可以自动将流里的东西转化成一些值，这些值由 » 指向的变量决定，如果上面我把amount的类型改成int，那么unit得到的值就会是”.9”
  • 最常见的分隔符是空格，可以想象成 » 操作的时候流遇到空格就切一下

state bits

input/output streams

manipulators