C style strings and operator overloading in C++

Question

I tried to overload the + operator on my own C styled version of string class.

Everything is fine except for the display() call for the second string s2 which displays garbage values.

class string_ {

   char *str;
   int len;

   public :
         ...
         void display()
         {
              cout << str;
         }
};

string_ :: string_()
{
   str = 0;
   len = 0;
}

string_ :: ~string_()
{
   delete []str;
   len = 0;
}


string_ :: string_(char *s,int l)
{
   len = l + 1; // +1 for \0
   str = new char[len];
   int i;
   for(i=0;i<len;i++)
          str[i] = s[i];
   str[i] = '\0';
}

string_ string_ :: operator +(string_ c)
{      
   int j = 0, i = 0;
   string_ s;
   s.len = len + c.len - 1;
   s.str = new char[s.len];
   while (str[i] != '\0')
   {s.str[i] = str[i]; i++;}

   while (c.str[j] != '\0')
   {s.str[i] = c.str[j]; i++; j++; }

   s.str[i] = '\0';
   //The below statements gives the desired output
   cout <<"\nIN operator +" << str;
   cout <<"\nIN operator +" << c.str;
   cout <<"\nIN operator +" << s.str;
   return s;
 }

int main()
{
   char *str = "Hello";
   char *str1 = " World";
   string_ s1(str,5);
   string_ s2(str1,6);
   string_ s3 = s1 + s2;
   cout << "\nstring s1 : ";
   s1.display();
   cout << "\nstring s2 : ";
   s2.display(); //PROBLEM
   cout << "\nConcatenated string : ";
   s3.display();
   return 0;
}

Answer 1

You are missing a proper copy-constructor where you clone the char-array from one string to another.

Also your operator+ should take a const-ref to your string class because a copy is not necessary here.

string_ string_ :: operator +(const string_& c)

The problem

Your 1st object has a pointer to a char-array, e.g. str=0x1. Because you have no copy-constructor the pointer-value is copied over automatically to the copy of your string. Two strings have now the same pointer. The first string deletes the array and the second will fail. Take a look at Rule of three which describes which functions should be implemented to avoid this problem. Edit: R Sahu was faster in the comments.

P.S. Since you use const-literals change char* to const char*.

P.S.2 Please post a MVCE next time.