Help, getting really strange errors!

Hello, I'm taking a C++ class, and I keep running into a strange occurrence. I'm writing a simulation program with people sending emails to one another and one of the requirements is we use abstract base classes when dealing with email forwarding strategies. The two ABC's in my project are EvaluateMessage and EvaluateRecipient. The Person class holds a pointer to each and when a Person is created a child class is chosen (based on an input file) to instantiate the pointers to. EvaluateMessage compiles and works just fine, however EvaluateRecipient is giving me problems and I don't know why. EvaluateRecipient works in other classes without a problem and the code all compiles and the input is all read fine, but when I include it in Person.h its gives me an error list this long in Visual Studio:

(The actual error list is much much longer but it's repetitive). I'm using guards in my header files, but reading the errors it seems that by add EvaluateRecipient to Person, I'm stripping all references of Person out of the project somehow. I don't know what's going on.

Errors:

Code:

---

1>evaluaterecipient.h(18): error C2065: 'Person' : undeclared identifier
1>evaluaterecipient.h(18): error C2059: syntax error : '>'
1>evaluaterecipient.h(18): error C2065: 'Person' : undeclared identifier
1>evaluaterecipient.h(18): error C2065: 'person' : undeclared identifier
1>evaluaterecipient.h(18): error C2143: syntax error : missing ',' before ')'
1>evaluaterecipient.h(19): error C2143: syntax error : missing ';' before '}'
1>evaluaterecipient.h(23): error C2143: syntax error : missing ';' before '{'
1>evaluaterecipient.h(28): error C2065: 'Person' : undeclared identifier
1>evaluaterecipient.h(28): error C2059: syntax error : '>'
1>evaluaterecipient.h(28): error C2065: 'Person' : undeclared identifier
1>evaluaterecipient.h(28): error C2065: 'person' : undeclared identifier
1>evaluaterecipient.h(28): error C2143: syntax error : missing ',' before ')'
1>evaluaterecipient.h(29): error C2143: syntax error : missing ';' before '}'
1>evaluaterecipient.h(33): error C2143: syntax error : missing ';' before '{'
1>evaluaterecipient.h(38): error C2065: 'Person' : undeclared identifier
1>evaluaterecipient.h(38): error C2059: syntax error : '>'
1>evaluaterecipient.h(38): error C2065: 'Person' : undeclared identifier
1>evaluaterecipient.h(38): error C2065: 'person' : undeclared identifier
1>evaluaterecipient.h(38): error C2143: syntax error : missing ',' before ')'
1>  EvaluateRecipient.cpp
1>person.h(36): error C2143: syntax error : missing ';' before '*'
1>person.h(36): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>person.h(36): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

---

EvaluateRecipient.h

Code:

---

#ifndef EVALUATE_RECIPIENT_H
#define EVALUATE_RECIPIENT_H

#include <list>
#include "Person.h"
#include "Message.h"

using namespace std;

class EvaluateRecipient
{
public:
        // Constructor
        EvaluateRecipient();

        virtual list<Person*> getList(Message* message, Person* person) = 0;
};

// Forward the message to all members of the contact list
class RStrategy1: public EvaluateRecipient
{
public:
        // Constructor
        RStrategy1();

        virtual list<Person*> getList(Message* message, Person* person);
};

// Forward the message to all members of the contact list except (possibly) the sender
class RStrategy2: public EvaluateRecipient
{
public:
        // Constructor
        RStrategy2();

        virtual list<Person*> getList(Message* message, Person* person);
};

// Forward the message to the "next" member on the person's contact list
class RStrategy3: public EvaluateRecipient
{
public:
        // Constructor
        RStrategy3();

        virtual list<Person*> getList(Message* message, Person* person);
};

#endif // EVALUATE RECIPIENT_H

---

Person.h

Code:

---

#ifndef PERSON_H
#define PERSON_H

#include <map>
#include <list>
#include <string>
#include "EvaluateMessage.h"
#include "EvaluateRecipient.h"

using namespace std;

class Person
{
public:
        // Constructor
        Person(string emailAddress);

        // Email of the person
        string email;

        // A list of strings (email addresses), or the Person object's contact list
        list<string> contactList;

        // A list of Message objects, the inbox of the Person object
        list<Message*> inbox;

        // A map that maps a MessageContent to an unsigned int
        map<MessageContent*, unsigned int> timesSeen;

        // Pointer to strategies
        // Forwarding strategy
        EvaluateMessage* mStrategy;

        EvaluateRecipient* rStrategy;

};

#endif // PERSON_H

---

Any help would be much appreciated, thanks!

Try to replace

Code:

---

#include "EvaluateRecipient.h"

---

in the person.h with the forward declaration:

Code:

---

class EvaluateRecipient;

---

and then insert

Code:

---

#include "EvaluateRecipient.h"

---

in the Person implementation file.

Quote:

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Originally Posted by Laketaco

Hello, I'm taking a C++ class, and I keep running into a strange occurrence.

---

There is nothing strange.

Look at your list of includes. Start with EvaluateRecipient.h:

Code:

---

#include <list>
#include "Person.h"

---

Now look at Person.h

Code:

---

#include <map>
#include <list>
#include <string>
#include "EvaluateMessage.h"
#include "EvaluateRecipient.h"

---

See the problem? In EvaluateRecipient.h, you are including Person.h, which includes EvaluateRecipient.h, which includes Person.h, which includes EvaluateRecipient.h, etc.

So it is an infinite recursion error. You usually solve this by using pointers to these objects and using forward declaration.

Secondly, don't put "using namespace std" in a header file. The reason is that if I were to use your header, you are forcing the entire std namespace into my C++ module. What if I don't want std namespace in my module, as it may cause compilation errors with other definitions I may have?

Instead, either prepend "std::" to the definitions that are in the std namespace (std::vector, std::list, etc), or state with the using clause exactly what you are using out of the std namespace:

Code:

---

using std::vector;
using std::list;
// etc.

---

Regards,

Paul McKenzie

Thank you guys so much, I figured it had something to do with infinite recursion I just couldn't figure out how to resolve it.

I'm coming from learning C# so I guess I took #include to mean the same as C#'s "using" when I guess C#'s keyword is a combined and simplified form of C++'s "using" and "class" keywords?

Excuse the double post but now I'm getting another error. I suspect it is once again due to me not setting up my hierarchy correctly. (Additionally if you have a link to a good hierarchy article I'd be much appreciated).

So I changed:

Code:

---

#include "EvaluateRecipient.h"

---

to the forward declaration:

Code:

---

class EvaluateRecipient;

---

and I recieved error "C2061: syntax error: identfier" in this block of code:

Code:

---

// Get the person's strategy on who to forward to in their contact list
                        inputFile >> tempInt;

                        switch(tempInt)
                        {
                        // Forward the message to all members of the contact list
                        case 1:
                                (people.back()->rStrategy) = new RStrategy1();
                                break;
                        // Forward the message to all members of the contact list except (possibly) the sender
                        case 2:
                                (people.back()->rStrategy) = new RStrategy2();
                                break;
                        // Forward the message to the "next" member on the person's contact list
                        case 3:
                                (people.back()->rStrategy) = new RStrategy3();
                                break;
                        // For error catching, sets the person's strategy to type 1
                        default:
                                (people.back()->rStrategy) = new RStrategy1();
                                break;
                        }

---

So I changed Person.h once again to include:

Code:

---

class RStrategy1;
class RStrategy2;
class RStrategy3;

---

and now I'm receiving error "C2512 : no appropriate default constructor available" in that same block instead. Is this because I included all child classes in the same header file as EvaluateRecipient? Also, why does EvaluateMessage get to be an "#include" instead of a forward declaration when its built almost exactly the same as EvaluateRecipient? (Note: EvaluateMessage doesn't compile if I try to make it a forward declaration instead of #include). Thanks for your patience.

It is enough with just a forward declaration if you just declare pointers to the type in question but whenever you use the type it has to be fully declared.

Have you included the needed headers in the cpp-file that doesn't compile?

- And that fixed it! I guess my concern at this point is that I'm taking an intro C++ and the teacher is really failing in all regards, and I really don't know how to set up a hierarchy properly and I know that's going to hurt me down the line. I'm going to Google the topic, but if any of you have a good article or link I'd be really grateful. Thank you all for your help!

I don't have any links but the general rule is to try to separate things as much as possible. Also, I guess the wisdom in how to achieve the perfect hierarchy has as many prophets as there are programmers... :)