Streams

Streams

stream: an abstraction for input/output. Streams convert between data and the string representation of data.

std::coutis an output stream .It has type std::ostream

Two ways to classify streams

By Direction:

• Input streams
• Output streams
• Input/Output streams

  By Source or Destination:

• Console streams
• File streams
• String streams

Output Streams

console

std::cout << 5 << std::endl;

file streams

std::ofstream out(“out.txt”)

Input Streams

• Each » ONLY reads until the next Whitespace
  • Whitespace = tab, space, newline
• Everything after the first whitespace gets saved and used the next time std::cin » is called
  • The place its saved is called a buffer!

    When things go wrong

    两个例子

    string str;  
    int x;  
    string otherStr;
    std::cin >> str >> x >> otherStr;  
    //what happens if input is blah blah blah?  
    std::cout << str << x << otherStr;
    //once an error is detected, the input stream’s  
    //fail bit is set, and it will no longer accept  
    //input
    

int age; double hourlyWage;  
cout << "Please enter your age: ";  
cin >> age;  
cout << "Please enter your hourly wage: ";  
cin >> hourlyWage;  
//what happens if first input is 2.17?

std::getline()

// Used to read a line from an input stream  
// Function Signature  
istream& getline(istream& is, string& str, char delim);

In contrast:

• “»” only reads until it hits
  whitespace (so can’t read a
  sentence in one go)
• BUT “»” can convert data to
  built-in types (like ints) while
  getline can only produce strings.
• AND “»” only stops reading at predefined whitespace while getline can stop reading at any delimiter you define ==IMPORTANT==: Don’t mix » with getline!

• reads up to the next whitespace character
  and does not go past that whitespace
  character.

• getline reads up to the next delimiter (by
  default, ‘\n’), and does go past that delimiter.
• TL;DR they don’t play nicely

  String streams

  If you only want to read OR write data:

• Read only: std::istringstream
• Give any data type to the istringstream, it’ll store it as
  a string!
• Write only: std::ostringstream
• Make an ostringstream out of a string, read from it
  word/type by word/type!
• Follows same patterns as the other i/ostreams!