Is this possible in C++? toString(ClassName* class) - c++

Question

I'd like to use toString with class argument, but for some reason there is an error.
The code is:
Animal.h
#include "Treatment.h"
#include "jdate.h"
#include <vector>
class Animal{
protected:
int id;
double weight;
int yy;
int mm;
int dd;
double accDose;
char sex;
vector<Treatment*> treatArray;
public:
Animal();
Animal(int newid, double newweight, int yy, int mm, int dd, char newsex, vector<Treatment*> treatArray);
~Animal();
};
Treatment.h
#ifndef TRE_H
#define TRE_H
#include <string>
#include <sstream>
#include "jdate.h"
#include "Animal.h"
#include "Cattle.h"
#include "Sheep.h"
class Treatment{
private:
int id;
jdate dayTreated;
double dose;
public:
Treatment(int id,jdate dayTreated, double dose);
Treatment();
~Treatment();
string toString(Animal* a);
};
#endif
Treatment.cpp
#include "Treatment.h"
using namespace std;
Treatment::Treatment(int newid,jdate newdayTreated, double newdose){
id=newid;
dayTreated = newdayTreated;
dose = newdose;
}
Treatment::Treatment(){
id=0;
dose=0;
}
Treatment::~Treatment(){}
string Treatment::toString(Animal* a)
{
string aa;
return aa;
}
toString is in Treatment class. I'm not sure but I think it's because Animal has
vector treatArray;. Does it actually matter?
Sorry that I cannot put the error messages here, because once I declare toString, for some reason tons of errors occur, such as
Error 1 error C2065: 'Treatment' : undeclared identifier l:\2011-08\c++\assignment\drug management\drug management\animal.h 30 1 Drug Management

Answer 1

// Animal.h
// #include "Treatment.h" remove this
class Treatmemt; // forward declaration
class Animal
{
...
};
In your version, Treatment.h and Animal.h include each other. You need to resolve this circular dependency using forward declaration. In .cpp files, include all necessary h-files.

Answer 2

You include Animal.h in Treatment.h before the class Treatment is defined, that's why you're getting the error.
Use forward declaration to solve this:
In Animal.h add line
class Treatment;

Answer 3

You've not used std namespace in both header files.
So, use std::string instead of string. Because string is defined in std namespace.
Simillarly use std::vector instead of vector.

Answer 4

There are a few problems with your code. First of all, Animal.h should have an include guard as Treatment.h has:
#ifndef ANIMAL_H
#define ANIMAL_H
// Your code here
#endif
I'd also suggest that you give a longer name to Treatment.h's guard, you'll reduce the risk of using the same name elsewhere.
Using guards will ensure that you don't have a circular inclusion. Still you do have a circular dependency because the Treatment class needs to know about the Animal class and vice versa. However, as in both cases you used pointers to the other class, the full definitions are not required and you can - should, actually - replace in both header files the inclusion of the other with a simple declaration. For instance in Animal.h remove
#include "Treatment.h"
and add
class Treatment;
Both Treatment.cpp and Animal.cpp must include both Treatment.h and Animal.h.