codice:
// Member function definitions for class String
#include <iostream>

using std::cout;
using std::endl;

#include <iomanip>

using std::setw;

#include <cstring>
#include <cassert>
#include "string1.h"

// Conversion constructor: Convert char * to String
String::String( const char *s ) : length( strlen( s ) )
{
   cout << "Conversion constructor: " << s << '\n';
   setString( s );         // call utility function
}

// Copy constructor
String::String( const String &copy ) : length( copy.length )
{
   cout << "Copy constructor: " << copy.sPtr << '\n';
   setString( copy.sPtr ); // call utility function
}

// Destructor
String::~String()
{
   cout << "Destructor: " << sPtr << '\n';
   delete [] sPtr;         // reclaim string
}

// Overloaded = operator; avoids self assignment
const String &String::operator=( const String &right )
{
   cout << "operator= called\n";

   if ( &right != this ) {         // avoid self assignment
      delete [] sPtr;              // prevents memory leak
      length = right.length;       // new String length
      setString( right.sPtr );     // call utility function
   }
   else
      cout << "Attempted assignment of a String to itself\n";

   return *this;   // enables cascaded assignments
}

const String &String::operator+( const String &right )
{
   cout << "operator= called\n";

   if ( &right != this ) {         // avoid self assignment
      delete [] sPtr;              // prevents memory leak
      length = right.length;       // new String length
      setString( right.sPtr );     // call utility function
   }
   else
      cout << "Attempted assignment of a String to itself\n";

   return *this;   // enables cascaded assignments
}

// Concatenate right operand to this object and
// store in this object.
const String &String::operator+=( const String &right )
{
   char *tempPtr = sPtr;        // hold to be able to delete
   length += right.length;      // new String length
   sPtr = new char[ length + 1 ]; // create space
   assert( sPtr != 0 );   // terminate if memory not allocated
   strcpy( sPtr, tempPtr );     // left part of new String
   strcat( sPtr, right.sPtr );  // right part of new String
   delete [] tempPtr;           // reclaim old space
   return *this;                // enables cascaded calls
}

// Is this String empty?
bool String::operator!() const { return length == 0; }

// Is this String equal to right String?
bool String::operator==( const String &right ) const
   { return strcmp( sPtr, right.sPtr ) == 0; }

// Is this String less than right String?
bool String::operator<( const String &right ) const
   { return strcmp( sPtr, right.sPtr ) < 0; }

// Return a reference to a character in a String as an lvalue.
char &String::operator[]( int subscript )
{
   // First test for subscript out of range
   assert( subscript >= 0 && subscript < length );

   return sPtr[ subscript ];  // creates lvalue
}

// Return a reference to a character in a String as an rvalue.
const char &String::operator[]( int subscript ) const
{
   // First test for subscript out of range
   assert( subscript >= 0 && subscript < length );

   return sPtr[ subscript ];  // creates rvalue
}

// Return a substring beginning at index and
// of length subLength
String String::operator()( int index, int subLength )
{
   // ensure index is in range and substring length >= 0
   assert( index >= 0 && index < length && subLength >= 0 );

   // determine length of substring
   int len;

   if ( ( subLength == 0 ) || ( index + subLength > length ) )
      len = length - index;
   else
      len = subLength;

   // allocate temporary array for substring and 
   // terminating null character
   char *tempPtr = new char[ len + 1 ];
   assert( tempPtr != 0 ); // ensure space allocated

   // copy substring into char array and terminate string
   strncpy( tempPtr, &sPtr[ index ], len );
   tempPtr[ len ] = '\0';

   // Create temporary String object containing the substring
   String tempString( tempPtr );
   delete [] tempPtr;  // delete the temporary array

   return tempString;  // return copy of the temporary String
}

// Return string length
int String::getLength() const { return length; }

// Utility function to be called by constructors and 
// assignment operator.
void String::setString( const char *string2 )
{
   sPtr = new char[ length + 1 ]; // allocate storage
   assert( sPtr != 0 );  // terminate if memory not allocated
   strcpy( sPtr, string2 );       // copy literal to object
}

// Overloaded output operator
ostream &operator<<( ostream &output, const String &s )
{
   output << s.sPtr;
   return output;   // enables cascading
}

// Overloaded input operator
istream &operator>>( istream &input, String &s )
{
   char temp[ 100 ];   // buffer to store input

   input >> setw( 100 ) >> temp;
   s = temp;        // use String class assignment operator
   return input;    // enables cascading
}

// Driver for class String
#include <iostream>

using std::cout;
using std::endl;

#include "string1.h"

int main()
{
   String s1( "happy" ), s2( " birthday" ), s3;

   // test overloaded equality and relational operators
   cout << "s1 is \"" << s1 << "\"; s2 is \"" << s2
        << "\"; s3 is \"" << s3 << '\"' 
        << "\nThe results of comparing s2 and s1:"
        << "\ns2 == s1 yields " 
        << ( s2 == s1 ? "true" : "false" )
        << "\ns2 != s1 yields " 
        << ( s2 != s1 ? "true" : "false" )
        << "\ns2 >  s1 yields " 
        << ( s2 > s1 ? "true" : "false" ) 
        << "\ns2 <  s1 yields " 
        << ( s2 < s1 ? "true" : "false" ) 
        << "\ns2 >= s1 yields "
        << ( s2 >= s1 ? "true" : "false" )
        << "\ns2 <= s1 yields " 
        << ( s2 <= s1 ? "true" : "false" );

   // test overloaded String empty (!) operator
   cout << "\n\nTesting !s3:\n";
   if ( !s3 ) {
      cout << "s3 is empty; assigning s1 to s3;\n";
      s3 = s1;              // test overloaded assignment
      cout << "s3 is \"" << s3 << "\"";
   }

   // test overloaded String concatenation operator
   cout << "\n\ns1 += s2 yields s1 = ";
   s1 += s2;                // test overloaded concatenation
   cout << s1;

   // test conversion constructor
   cout << "\n\ns1 += \" to you\" yields\n";
   s1 += " to you";         // test conversion constructor
   cout << "s1 = " << s1 << "\n\n";

   // test overloaded function call operator () for substring
   cout << "The substring of s1 starting at\n"
        << "location 0 for 14 characters, s1(0, 14), is:\n"
        << s1( 0, 14 ) << "\n\n";

   // test substring "to-end-of-String" option
   cout << "The substring of s1 starting at\n"
        << "location 15, s1(15, 0), is: "
        << s1( 15, 0 ) << "\n\n";  // 0 is "to end of string"

   // test copy constructor
   String *s4Ptr = new String( s1 );  
   cout << "*s4Ptr = " << *s4Ptr << "\n\n";

   // test assignment (=) operator with self-assignment
   cout << "assigning *s4Ptr to *s4Ptr\n";
   *s4Ptr = *s4Ptr;          // test overloaded assignment
   cout << "*s4Ptr = " << *s4Ptr << '\n';

   // test destructor
   delete s4Ptr;     

   // test using subscript operator to create lvalue
   s1[ 0 ] = 'H';      
   s1[ 6 ] = 'B';
   cout << "\ns1 after s1[0] = 'H' and s1[6] = 'B' is: "
        << s1 << "\n\n";

   // test subscript out of range
   cout << "Attempt to assign 'd' to s1[30] yields:" << endl;
   s1[ 30 ] = 'd';     // ERROR: subscript out of range

   return 0;
}
Da questo codice dovrei fare un overloadning che mi permetta di eseguire l'operazione

Stringa1 = stringa2 + strnga3; senza modificare gli oggetti stranga2 e stringa3.

Però se io creo l'oggetto dentro al funziona, all'uscitta della funzione l'oggetto creato mi viene automaticamente distrutto giusto?

Quindi come potri fare per mantenere la copia?

Grazie