Dear Friends:
I need some help to identify the error.
When I compile my application I get the following error message:
Error 1 error C2678: binary '==' : no operator found which takes a left-hand operand of type 'extPersonType' (or there is no acceptable conversion) f:\college material\cs270\sourcecode\addressbook\addressbook\arrayListType.h 251 1 AddressBook
Any help will be greatly appreciated,
Dani
What's the code at that line?
You will need to write an override for == for your extPersonType, or revise your code to compare members of that type which are basic data types.
Both of the above replies are basically correct.
Thanks , here is the code:
My addressBookType Class:
#ifndef H_addressBookType
#define H_addressBookType
#include "arrayListType.h"
using namespace std;
template <class extPersonType>
class addressBookType : public arrayListType<elemType>
{
public:
addressBookType(int size = 500); //Increase the default size from 100 to 500
const arrayListType<extPersonType>& operator= (const arrayListType<extPersonType>&);
/*int searchByLastName(string lname) const;
void print() const;
void printNameBetweenDate(int startMonth, int startDay, int startYear, int endMonth, int endDay, int endYear) const;
void printNameInAGroup(string grp) const;
void printNameBetweenNames(string startName, string endName) const;*/
private:
};
template <class extPersonType>
addressBookType<extPersonType>::addressBookType(int size):arrayListType(size)
{
if (size < 0)
{
cerr << "The array size must be positive. Creating "
<< "an array of size 500. " << endl;
maxSize = 500;
}
else
maxSize = size;
length = 0;
list = new extPersonType[maxSize];
assert(list != NULL);
}
template <class extPersonType>
const addressBookType<extPersonType>& addressBookType<extPersonType>::operator= (const addressBookType<extPersonType>& otherList)
{
if (this != &otherList) //avoid self-assignment
{
delete [] list;
maxSize = otherList.maxSize;
length = otherList.length;
list = new extPersonType[maxSize]; //create the array
assert(list != NULL); //if unable to allocate memory
//space, terminate the program
for (int i = 0; i < length; i++)
list[i] = otherList.list[i];
}
return *this;
}
#endif
I guess you overwrite the '=', but you don't overwrite the '=='.
As I can see in your code, you're comparing them classes.
You can't compare if the tomato is a melon.
But you can compare if the tomato has as many seeds inside of it as the melon.
You're using '!=', so you need to overwrite the '==' comparison operator.
!= is just the NOT operator of equality.
Then you can just do:
if( !(tomato == melon) ) {
// stuff happens here..
}
Just to be sure..
But I guess you already know that, especially after rubberman's answer. :)
Good luck!
Thank you all for your assisntance.
I understand that I need to overwrite the == function. I understand that I can't compare the class as a whole to another class because they aren't the same type, so I have to go deeper and compare elements within the class. The problem comes from understanding the syntax for identifying the two object types that I want to compare. If I first define the function as such:
const arrayListType<extPersonType>& operator==(const arrayListType<extPersonType>&) const;
The class that I am placing the overwrite function is in the addressBookType, which is overwriting the arrayListType. The book doesn't provide clarification on exactly what class I am adding. I am assuming that it should be the class name where the overwrite is being performed, but since I want to use many of the functions that are available within the arrayListType function then I figured that I must somehow switch the object types so that is understands what it is reading.
This is where I am getting lost. In my addressBookType, what should be within the override operator== function, and how does this allow the arrayListType class to understand the object and perform the various tasks that will be asked.
I'm hoping I am explaining this correctly. I would still like to successfully complete the task as well as the following task that goes with it. I just need some sample code to clear up what I am missing.
Again, thank you so much for all your help.
Dani
Comparison of non-identical types is not simple. You need to know which elements of each should be compared. In truth, this is an equivalence function. Create a class::compare(const otherclass& other) function and then iterate through the instances (this and other) until they don't compare equal, and return 1 or -1 as appropriate, otherwise at the end return 0. Use this compare function in the operator== and operator!= functions, and return true/false as appropriate.
Thank ypu so much.
I don’t know which way is correct with class templates:
#include <iostream>
#include <cassert>
using namespace std;
//Definition of a node
template <class Type>
struct nodeType
{
Type info;
nodeType<Type> *link;
};
template <class Type>
class linkedListHeadTrail
{
public:
linkedListHeadTrail(); //Constructor - link = NULL
void clearAll(); //Clear all items in the list
void print(); //Print the content of the linked list
void listLength(); //Print the number of items stored in the list
void insertAt(int position, const Type& value); //Insert an item at the designated position
void removeAt(int position); //Remove an item at the designated position
protected:
nodeType<Type> *head; //Points to the first item in the list
nodeType<Type> *trail; //Points to the last item in the list
//nodeType* current; //Contains the current item within the list
int listLen; //Number of items within the list
};
template <class nodeType>
linkedListHeadTrail<nodeType>::linkedListHeadTrail() //Default Constructor
{
head = NULL;
trail = NULL;
listLen = 0;
}
template <class nodeType>
linkedListHeadTrail<nodeType>::clearAll()
{
//Move all elements from the list
nodeType<Type>* prog; ------- Error with TYPE
}
OR:
#include <iostream>
#include <cassert>
using namespace std;
//Definition of a node
template <class Type>
struct nodeType
{
Type info;
nodeType<Type> *link;
};
template <class Type>
class linkedListHeadTrail
{
public:
linkedListHeadTrail(); //Constructor - link = NULL
void clearAll(); //Clear all items in the list
void print(); //Print the content of the linked list
void listLength(); //Print the number of items stored in the list
void insertAt(int position, const Type& value); //Insert an item at the designated position
void removeAt(int position); //Remove an item at the designated position
protected:
nodeType<Type> *head; //Points to the first item in the list
nodeType<Type> *trail; //Points to the last item in the list
//nodeType* current; //Contains the current item within the list
int listLen; //Number of items within the list
};
template <class Type>
linkedListHeadTrail<Type>::linkedListHeadTrail() //Default Constructor
{
head = NULL;
trail = NULL;
listLen = 0;
}
template <class Type>
linkedListHeadTrail<Type>::clearAll()
{
//Move all elements from the list
nodeType<Type>* prog; ------------ Error with TYPE
}
Doesn’t seem to matter which way I use, neither are working. I initially wrote it using the second method, but have an error which is stopping me from moving on. I get the same error at the same line. Can you please enlighten me?
Best Wishes,
Dani
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