SavantStrike
October 4th, 2010, 03:05 AM
EDIT: edited to add entire source code and not just part of it.
I'm almost done with a program I need to write for class, and it runs (and does everything it's expected to do), but I'm scratching my head as to why it runs because one of the functions cannot return a value (compiler error if I try to make it return a value), yet it works.
I wrote a non templated version of the same program and the same class, and I can return *this just fine. But this problem required I do the same thing with a template.
returning *this in the overloaded= operator function causes the following error:
driver.cc: In member function ‘const T& myList<T>::operator=(const myList<T>&) [with T = int]’:
driver.cc:110: instantiated from here
driver.cc:95: error: invalid initialization of reference of type ‘const int&’ from expression of type ‘myList<int>’
#include <iostream>
using std::cout;
using std::endl;
using std::string; //needed to handle non integer types
#ifndef TmyList_h
#define TmyList_h
template<class T> class myList
{
public:
myList(); //default constructor
void printall();
template<class TT> //needed to overload +
//the + operator is not a member of the myList class because it is a friend
//therefore, a second template is needed, the previously defined template <class TT>
friend myList<TT> &operator+(myList<TT> &, const TT &);
const T &operator=(const myList &);
int &operator[](int);
~myList(); //destructor
private:
int size;//integer to control size or array
T *ptr; //pointer to array
};
template<class T>
myList<T>::myList(){
size = 0; //setting left variable to zero means array will have zero elements
ptr = NULL; //set ptr to null because the array is empty
}
template<class T>
void myList<T>::printall(){
int counter = 0; //temporary counter used for printing the elements of the array referenced by ptr
while (counter < size){ // loop which runs from 0 to j where j is the last element of the array referenced by ptr
//and n is the element of the array at the position "counter"
cout << *(ptr + counter) << " ";//print out the value of array[n]
counter++; //increment counter to the next position in the array
}//all of the elements in the array that ptr references have been printed to the screen
cout << endl;
}
template<class T>
myList<T> &operator+(myList<T> &left, const T &right){
if (left.ptr == NULL){
left.size = left.size + 1;
left.ptr = new T[left.size];
left.ptr[(left.size - 1)] = right;
return left;
}
else{
int *tmpArray = new T[left.size]; //create a new array for deep copy operation
//deep copy values in pointer to tmpPointer
for(int i=0; i<(left.size); i++){
tmpArray[i] = *(left.ptr + i);
}
delete [] left.ptr; //deallocate ptr
left.size++; //a new array will be created with one extra element
//reallocate pointer to point to a larger array
left.ptr = new T[left.size];
//deep copy tmpArray into the array referenced by ptr
for(int i=0; i<(left.size-1); i++){//stop at one less than the new size, as tmpArray is one element smaller than the array referenced by ptr
left.ptr[i] = tmpArray[i];
}
left.ptr[(left.size-1)] = right; //add the last element to the array referenced by ptr
delete[] tmpArray; //deallocate tmpArray
return left;
}
}
template <class T>
int &myList<T>::operator[](int index){
return ptr[index];
}
template <class T>
const T &myList<T>::operator=(const myList &right){
if(&right !=this){ //check for self assignment
if (size != right.size){ //then the array in the list on the left of the = operator must be expanded
delete [] ptr; //delete original array in memory
size = right.size; //increment size by 1
ptr = new int[size]; //create a new array one unit larger
}
for (int i=0; i<size; i++){
ptr[i]=right.ptr[i]; //set each element [n] in the array in the left hand object to the value at [n] in right hand object
}
}
return *this; //this line causes the error
}
template<class T>
myList<T>::~myList(){
size = 0;
delete [] ptr;
}
#endif
int main ()
{
myList<int> a;
a.printall();
a= a + 10;
a= a + 5;
a.printall();
a[0]=a[1];
a.printall();
return 0;
}
Any help would be appreciated as I'm still not sure I've 100 percent grasped what I did with this code... I understood it better without forcing it into a template.
It would also be nice to hand it in without a comment stating I can't return *this like I'm supposed to :P.
TIA
I'm almost done with a program I need to write for class, and it runs (and does everything it's expected to do), but I'm scratching my head as to why it runs because one of the functions cannot return a value (compiler error if I try to make it return a value), yet it works.
I wrote a non templated version of the same program and the same class, and I can return *this just fine. But this problem required I do the same thing with a template.
returning *this in the overloaded= operator function causes the following error:
driver.cc: In member function ‘const T& myList<T>::operator=(const myList<T>&) [with T = int]’:
driver.cc:110: instantiated from here
driver.cc:95: error: invalid initialization of reference of type ‘const int&’ from expression of type ‘myList<int>’
#include <iostream>
using std::cout;
using std::endl;
using std::string; //needed to handle non integer types
#ifndef TmyList_h
#define TmyList_h
template<class T> class myList
{
public:
myList(); //default constructor
void printall();
template<class TT> //needed to overload +
//the + operator is not a member of the myList class because it is a friend
//therefore, a second template is needed, the previously defined template <class TT>
friend myList<TT> &operator+(myList<TT> &, const TT &);
const T &operator=(const myList &);
int &operator[](int);
~myList(); //destructor
private:
int size;//integer to control size or array
T *ptr; //pointer to array
};
template<class T>
myList<T>::myList(){
size = 0; //setting left variable to zero means array will have zero elements
ptr = NULL; //set ptr to null because the array is empty
}
template<class T>
void myList<T>::printall(){
int counter = 0; //temporary counter used for printing the elements of the array referenced by ptr
while (counter < size){ // loop which runs from 0 to j where j is the last element of the array referenced by ptr
//and n is the element of the array at the position "counter"
cout << *(ptr + counter) << " ";//print out the value of array[n]
counter++; //increment counter to the next position in the array
}//all of the elements in the array that ptr references have been printed to the screen
cout << endl;
}
template<class T>
myList<T> &operator+(myList<T> &left, const T &right){
if (left.ptr == NULL){
left.size = left.size + 1;
left.ptr = new T[left.size];
left.ptr[(left.size - 1)] = right;
return left;
}
else{
int *tmpArray = new T[left.size]; //create a new array for deep copy operation
//deep copy values in pointer to tmpPointer
for(int i=0; i<(left.size); i++){
tmpArray[i] = *(left.ptr + i);
}
delete [] left.ptr; //deallocate ptr
left.size++; //a new array will be created with one extra element
//reallocate pointer to point to a larger array
left.ptr = new T[left.size];
//deep copy tmpArray into the array referenced by ptr
for(int i=0; i<(left.size-1); i++){//stop at one less than the new size, as tmpArray is one element smaller than the array referenced by ptr
left.ptr[i] = tmpArray[i];
}
left.ptr[(left.size-1)] = right; //add the last element to the array referenced by ptr
delete[] tmpArray; //deallocate tmpArray
return left;
}
}
template <class T>
int &myList<T>::operator[](int index){
return ptr[index];
}
template <class T>
const T &myList<T>::operator=(const myList &right){
if(&right !=this){ //check for self assignment
if (size != right.size){ //then the array in the list on the left of the = operator must be expanded
delete [] ptr; //delete original array in memory
size = right.size; //increment size by 1
ptr = new int[size]; //create a new array one unit larger
}
for (int i=0; i<size; i++){
ptr[i]=right.ptr[i]; //set each element [n] in the array in the left hand object to the value at [n] in right hand object
}
}
return *this; //this line causes the error
}
template<class T>
myList<T>::~myList(){
size = 0;
delete [] ptr;
}
#endif
int main ()
{
myList<int> a;
a.printall();
a= a + 10;
a= a + 5;
a.printall();
a[0]=a[1];
a.printall();
return 0;
}
Any help would be appreciated as I'm still not sure I've 100 percent grasped what I did with this code... I understood it better without forcing it into a template.
It would also be nice to hand it in without a comment stating I can't return *this like I'm supposed to :P.
TIA