String (C++ class)

Basics

• string header #include <string>

• Constructors

• Common methods

  • at() returns a reference variable so you can assign value to it!

  • size()/length()

  • operator+() allows str1 + str2

  • clear() clears the content of a string

  • empty() check empty

• I/O

  • read from cin

    • >> extraction

    • getline

      // when a getline is used after >>
      // to avoid reading in an empty string
      
      int val1;
      string restOfTheLine;
      
      // method 1, recommended in projects
      cin >> val1;
      do {
        getline(cin, restOfTheLine);
      } while (restOfTheLine.empty());
      
      // method 2, cin.ignore()
      cin >> val1;
      // cin.ignore();  // usually enough, clear up to 1 character till the new line
      cin.ignore(numeric_limits<streamsize>::max(), '\n');  // clear all till the new line
      getline(cin, restOfTheLine);
      
      // method 3, the std::ws manipulate
      cin >> val1;
      getline(cin >> ws, restOfTheLine);
      
      // method 3a
      cin >> val1 >> ws;
      getline(cin, restOfTheLine);
      

  • write to terminal

    • << insertion

• string algorithms

  • most are similar to 1d array

Advanced

• More methods

  • string::find() find the first occurrence of a character or a sub-string

  • string::substr() extract a sub-string

  • string::push_back() add a character at the end

  • string::insert() insert a string to a position

  • string::replace() replace a sub-string with a string

  • std::to_string() convert a numeric value to a string

  • std::stoi(), std::stod() convert a string to an int or double value

• Extract data from a string (parsing)

  • alternative method: istringstream

• Generate (formatted) text based on data

  • alternative method: ostringstream

// Patient data with name, age and gender formatted as a string like
//   John Smith, 21, Male

class Patient {
  string name;
  age int;
  string gender;
 public:
  void parse(const string &text);
  string toStr();
}

void Patient::parse(const string &text) {
  int firstComma = text.find(',');
  int secondComma = text.find(',', firstComma + 1);
  name = text.substr(0, firstComma);
  age = stoi(text.substr(firstComma + 2, secondComma - firstComma - 2));
  gender = text.substr(secondComma + 2, text.length() - secondComma -2);
}

void Patient::toStr() {
  return "Name: " + name + " | Age: " + to_string(age) + " | Gender: " + gender";
}