Lab 5 (Our very own string class)

Programming Workshop 2 (CSCI 1061U)

Winter 2021

Faculty of Science

Ontario Tech University

Introduction

We all love the std::string class. Now lets make our own string class. The goal today is to create a simple str class that mimic the functionality of the std::string class. To keep things civilized, I have taken the liberty of implementing part of the str class. You are asked to complete the rest of the functions.

Task

Please implement your functions in the str.cpp class.

Header file declaring str class.

// str.h

#ifndef __str_h__
#define __str_h__

#include <iostream>
#include <string>
#include <math.h>

using namespace std;


class str
{
  protected:
  char* _buf;  // pointer to the underlying storage
  int _n;      // size of the buffer

  public:
  
  // constructors of various forms
  str();      
  str(int n);  
  str(char ch);
  str(const char* c_str);

  // lets not forget the destructor
  ~str();

  // inline functions for finding length info of the str
  inline const int& length() const { return _n; }
  inline bool is_empty() const { return length() == 0; }

  // index operators
  char& operator[](int i) { return _buf[i]; }
  const char& operator[](int i) const { return _buf[i]; }
  
  // TODO 1. You need to implement the assignment operator
  const str& operator=(const str& s);

  // TODO 2. You need to implement the + operator concatenates two str
  friend str operator+(const str& a, const str& b);

  friend ostream& operator<<(ostream& os, const str& s);
  friend istream& operator>>(istream& is, str& s);
};

#endif

Meanwhile the str.cpp file looks like

// str.cpp

#include "str.h"

str::str() : _n(0), _buf(0)
{}

str::str(int n) : _n(n)
{
  _buf = new char[_n];
}

str::str(char ch) : _n(1)
{
  _buf = new char[_n];
  _buf[0] = ch;
}

str::str(const char* c_str)
{
  _n = strlen(c_str);
  _buf = new char[_n];
  for (int i=0; i<_n; ++i) _buf[i]=c_str[i];
}

str::~str()
{
  if (_buf) delete [] _buf;
}

ostream& operator<<(ostream& os, const str& s)
{
  if (!s.is_empty()) {
    for (int i=0; i<s.length(); ++i) {
      cout << s[i];
    }
  }
  else cout << "[null str]";
  
  return os;
}

istream& operator>>(istream& is, str& s)
{
  char ch;
  do {
    ch = is.get();
    if (ch == ' ' || ch == '\n') break;
    s = s + ch;
  } while(true);

  return is;
}

// 1. TODO - assignment operator

// 2. TODO - concatenation operator

And the main.cpp is

// main.cpp

#include "str.h"

int main()
{
  str s1; 
  cout << s1 << endl;
  
  str s2("Hello"); 
  cout << s2 << endl;
  
  str s3("World");

  str s4 = s2 + " " + s3;
  cout << s4 << endl;

  str s5, s6;
  cin >> s5 >> s6;
  cout << s5 << ' ' << s6;
  
  return 0;
}

When I compile (g++ main.cpp str.cpp -o str), and run the code I get the following output

$ ./str <---- user
[null str]
Hello
Hello World
123 345 <---- user
123 345

Submission

Please submit str.h and str.cpp files via Canvas.