Why doesn't the compiler like all the strings that are associated with "Iter"?

Question

I am implementing one of the behavioral design patterns.

The compiler gives errors in lines that are related to "Iter". I don't understand at all why this happens, and even more so, how can it be fixed?

I thought that maybe there was a clerical error somewhere (I'm doing a program following the example from the book, the code is a screenshot and needs to be retyped) - but there is no clerical error, everything is exactly as there.

So what could be the problem?

I suspect it's something simple that is not immediately apparent to me because of my low level of knowledge.

Errors:

main.cpp:57:2: error: ‘Iter’ does not name a type
  Iter* createIterator() const;
  ^~~~
main.cpp:98:41: error: no ‘Iter* ContainerPerson::CreateIterator() const’ member function declared in class ‘ContainerPerson’
 Iter* ContainerPerson::CreateIterator() const {
                                         ^~~~~
main.cpp: In function ‘int main()’:
main.cpp:113:18: error: ‘class ContainerPerson’ has no member named ‘createIterator’
  Iter* it = list.createIterator();
                  ^~~~~~~~~~~~~~
main.cpp:118:10: error: invalid use of non-static member function ‘void Iter::first()’
  for(it->first; !it->isDoneBegin(); it->next()) {
      ~~~~^~~~~
main.cpp:69:7: note: declared here
  void first() {
       ^~~~~
main.cpp:124:10: error: invalid use of non-static member function ‘void Iter::first()’
  for(it->first; !it->isDoneBegin(); it->prev()) {
      ~~~~^~~~~
main.cpp:69:7: note: declared here
  void first() {
       ^~~~~

Full code:

#include <iostream>
#include <string>
using namespace std;

class Person {
public: 
    string name;
    int age;
    string address;

    Person() {
        name = "";
        age = 0;
        address = "";
    }
    
    Person(string n, int a, string ad) {
        name = n;
        age = a;
        address = ad;
    }

    void prn() {
        cout << "Информация о человеке:";
        cout << "\n Фамилия: " << name;
        cout << "\t Возраст: " << age;
        cout << "\n Город: " << address;
    }
};

class ContainerPerson {
public:
    Person* masPerson;
    int currentpos;

    ContainerPerson(int size) {
        masPerson = new Person[size];
        currentpos = - 1;
    }

    ~ContainerPerson() {
        delete []masPerson;
    }

    void add(Person *obj) {
        int pos = ++currentpos;
        masPerson[pos].name = obj->name;
        masPerson[pos].age = obj->age;
        masPerson[pos].address = obj->address;
    }

    bool isEmpty() {
        return (currentpos == - 1);
    }

    friend class Iter;
    Iter* createIterator() const;
};

class Iter {
    const ContainerPerson* container;
    int index;

public:
    Iter(const ContainerPerson* con) {
        container = con;
    }
    
    void first() {
        index = 0;
    }

    void end() {
        index = container->currentpos;
    }

    void next() {
        index++;
    }

    void prev() {
        index--;
    }

    bool isDoneEnd() {
        return (index == container->currentpos + 1);
    }

    bool isDoneBegin() {
        return (index == -1);
    }

    Person currentItem() {
        return container->masPerson[index];
    }
};

Iter* ContainerPerson::CreateIterator() const {
    return new Iter(this);
}

int main() {
    setlocale(LC_ALL, "Russian");
    ContainerPerson list(7);
    list.add(new Person("Sur1", 26, "City1"));  
    list.add(new Person("Sur2", 33, "City2"));
    list.add(new Person("Sur3", 65, "City3"));
    list.add(new Person("Sur4", 43, "City4"));
    list.add(new Person("Sur5", 58, "City5"));
    list.add(new Person("Sur6", 47, "City6"));
    list.add(new Person("Sur7", 32, "City7"));
    
    Iter* it = list.createIterator();
    Person currentPerson;   
    

    cout << "\nOutput (beg-next):";
    for(it->first; !it->isDoneBegin(); it->next()) {
        currentPerson = it->currentItem();
        currentPerson.prn();
    }

    cout << "\nOutput (beg-prev):";
    for(it->first; !it->isDoneBegin(); it->prev()) {
        currentPerson = it->currentItem();
        currentPerson.prn();
    }

    return 0;
}

Answer 1

1. You need a forward declaration class Iter; outside the declaration of class ContainerPerson . Otherwise the friend class is ContainerPerson::Iter which is unrelated to the Iter you declare later. See Why does a C++ friend class need a forward declaration only in other namespaces?

2. Typo in the definition of Iter* ContainerPerson::CreateIterator() : should be createIterator , with lower case c .

3. Typo in for(it->first; ...) ; should be it->first() .

4. Your iterations are mixed up. They should be

    for(it->first(); !it->isDoneEnd(); it->next()) {
        // ...
    }
    for(it->end(); !it->isDoneBegin(); it->prev()) {
        // ...
    }

With these fixed it compiles and runs cleanly: https://godbolt.org/z/3K7T7d14h

Bonus bug for you to fix later: You never delete the Iter which is allocated in ContainerPerson::createIterator() . That's a memory leak.

Answer 2

main.cpp:57:2: error: ‘Iter’ does not name a type
  Iter* createIterator() const;
  ^~~~

Though this declaration of a friend class

friend class Iter;

appears in the definition of the class ContainerPerson nevertheless the name Iter is not visible in the scope of the class ContainerPerson .

So the compiler issues an error for this member function declaration.

You need either to declare the class Iter before the class ContainerPerson . For example

class Iter;

class ContainerPerson
{
    //...
    friend class Iter;
    Iter* createIterator() const;
    //...
};

Or to use an elaborated type specifier in the return type in the function declaration like

class ContainerPerson
{
    //...
    friend class Iter;
    class Iter* createIterator() const;
    //...
};


main.cpp:98:41: error: no ‘Iter* ContainerPerson::CreateIterator() const’ member function declared in class ‘ContainerPerson’
 Iter* ContainerPerson::CreateIterator() const {
                                         ^~~~~

You declared the member function

Iter* createIterator() const;
      ^^

not the member function

Iter* CreateIterator() const;
      ^^


main.cpp: In function ‘int main()’:
main.cpp:113:18: error: ‘class ContainerPerson’ has no member named ‘createIterator’
  Iter* it = list.createIterator();
                  ^~~~~~~~~~~~~~

This error is a consequence of the first error.

As for these errors

main.cpp:118:10: error: invalid use of non-static member function ‘void Iter::first()’
  for(it->first; !it->isDoneBegin(); it->next()) {
      ~~~~^~~~~

and

main.cpp:124:10: error: invalid use of non-static member function ‘void Iter::first()’
  for(it->first; !it->isDoneBegin(); it->prev()) {
      ~~~~^~~~~

then it seems you mean a function call

it->first()