Importance of copy constructor

String class in C++ Without copy constructor

#include<iostream>

#include<cstring>

using namespace std;

class String

{

private:

char *s;

int size;

public:

String( char *str = NULL); // constructor

void print() { cout << s << endl; }

void change(const char *); // Function to change

};

String::String( char *str)

{

size = strlen(str);

s = new char[size+1];

strcpy(s, str);

}

void String::change(const char *str)

{

delete [] s;

size = strlen(str);

s = new char[size+1];

strcpy(s, str);

}

int main()

{

String str1("mice");

String str2 = str1;

str1.print(); // what is printed ?   mice

str2.print(); // what is printed ?   mice

str2.change("Udupi");

str1.print(); // what is printed now ? Udupi

str2.print(); // what is printed now ? Udupi

return 0;

}

String class in C++ With copy constructor

#include<iostream>

#include<cstring>

using namespace std;

class String

{

private:

char *s;

int size;

public:

String( char *str = NULL); // constructor

String( String &ss);  //copy constructor

~String() { delete [] s; }// destructor

void print() { cout << s << endl; }

void change(const char *); // Function to change

};

String::String( String &ss)  

{

    size = strlen(ss.s);

s = new char[size+1];

strcpy(s, ss.s);

}

String::String( char *str)

{

size = strlen(str);

s = new char[size+1];

strcpy(s, str);

}

void String::change(const char *str)

{

delete [] s;

size = strlen(str);

s = new char[size+1];

strcpy(s, str);

}

int main()

{

String str1("mice");

String str2 = str1;

str1.print(); // what is printed ?   mice

str2.print(); // what is printed ?   mice

str2.change("Udupi");

str1.print(); // what is printed now ? mice

str2.print(); // what is printed now ? Udupi

return 0;

}