Multiple class in a list c++ [duplicate] - c++

Question

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Why can templates only be implemented in the header file?
Main class
int main() {
initCarList();
}
void initCarList() {
List<Car> carList;
Car c1 = Car("Toyota", "Bettle", 5);
carList.add(c1);
Car c2 = Car("Mercedes", "Bettle", 7);
carList.add(c2);
Car c3 = Car("FireTruck", "Large Van", 20);
carList.add(c3);
Car c4 = Car("Puma", "Saloon Car", 10);
carList.add(c4);
}
List class
#include "List.h"
#include <iostream>
using namespace std;
template <typename ItemType>
class List {
private:
ItemType itemList[10];
int size;
public:
List();
void add(ItemType);
void del(int index);
bool isEmpty();
ItemType get(int);
int length();
};
template<typename ItemType>
List<ItemType>::List() {
size = 0;
}
template<typename ItemType>
void List<ItemType>::add(ItemType item) {
if(size < MAX_SIZE) {
itemList[size] = item;
size++;
} else {
cout << typename << " list is full.\n";
}
}
I got errors like these
Error 3 error LNK2019: unresolved external symbol "public: void
__thiscall List::add(class Car)" (?add#?$List#VCar####QAEXVCar###Z) referenced in function "void
__cdecl initCarList(void)" (?initCarList##YAXXZ) C:\Users\USER\Desktop\New
folder\DSA_Assignment\main.obj DSA_Assignment
Did I do anything wrongly in my code? NEED HELP THANKS!

Answer 1

There is a syntax error (cout << typename ) in your code. I don't know how you got the linker error. May be its not being compiled at all.
otherwise its okay http://ideone.com/PGWGZu

Answer 2

Clearly you did as it doesn't work! Flippancy aside, let's take a look at the error message bit by bit:
Error 3 error LNK2019: unresolved external symbol
So this is a linkage error. The linker is trying to put together the units that were individually compiled together, but in this case it can't find an external symbol - usually a function or variable name.
"public: void __thiscall List::add(class Worker)" (?add#?$List#VWorker####QAEXVWorker###Z)
This is the full signature of the function that you're missing. It's name manged unfortunately but with your context knowledge of the code that you're writing, you should be able to tell that it's:
void List::add(Worker)
The next bit ...
referenced in function "void __cdecl initWorkerList(void)" (?initWorkerList##YAXXZ) C:\Users\USER\Desktop\New folder\DSA_Assignment\main.obj DSA_Assignment
... is telling you where the problem is happening, i.e where in the code it's trying to link, there is a reference to the missing function. Again, after demangling it's in:
void initWorkerList()
As you can see, with a bit of graft, you can determine exactly what you've done wrong here. Hope this helps.