Da questo codice dovrei fare un overloadning che mi permetta di eseguire l'operazionecodice:// 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 © ) : 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; }
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
Rispondi quotando
perator+=( const String &right )