为什么以下函数可以在不声明为友元或成员函数的情况下访问类成员

头文件：

// pe10-8arr.h -- header file for a simple list class
#ifndef SIMPLEST_
#define SIMPLEST_
// program-specific declarations
const int TSIZE = 45;      // size of array to hold title
struct film
{
    char title[TSIZE];
    int rating;
};
// general type definitions
typedef struct film Item;
const int MAXLIST = 10;
class simplist
{
private:
    Item items[MAXLIST];
    int count;
public:
    simplist(void);
 bool isempty(void);
 bool isfull(void);
    int itemcount();
 bool additem(Item item);
    void transverse( void (*pfun)(Item &item));
};
#endif

使用标题的代码：

#include "pe10-8arr.h"
simplist::simplist(void)
{
    count = 0;
}
bool simplist::isempty(void)
{
    return count == 0;
}
bool simplist::isfull(void)
{
    return count == MAXLIST;
}
int simplist::itemcount()
{
    return count;
}
bool simplist::additem(Item item)
{
    if (count == MAXLIST)
        return false;
    else
        items[count++] = item;
    return true;
}
void simplist::transverse( void (*pfun)(Item &item))
{
    for (int i = 0; i < count; i++)
        (*pfun)(items[i]);
}
#include <iostream>
#include <cstdlib>         // prototype for exit()
#include "pe10-8arr.h"     // simple list class declaration
                                // array version
void showmovies(Item &item); // to be used by transverse()
int main(void)
{
    using namespace std;
    simplist movies;     // creates an empty list
    Item temp;
    if (movies.isfull())    // invokes isfull() member function
    {
        cout << "No more room in list! Bye!n";
        exit(1);
    }
    cout << "Enter first movie title:n";
    while (cin.getline(temp.title,TSIZE) && temp.title[0] != '')
    {
        cout << "Enter your rating <0-10>: ";
        cin >> temp.rating;
        while(cin.get() != 'n')
            continue;
        if (movies.additem(temp) == false)
        {
            cout << "List already is full!n";
            break;
        }
        if (movies.isfull())
        {
            cout << "You have filled the list.n";
            break;
        }
        cout << "Enter next movie title (empty line to stop):n";
    }
    if (movies.isempty())
        cout << "No data entered. ";
    else
    {
        cout << "Here is the movie list:n";
        movies.transverse(showmovies);
    }
    cout << "Bye!n";
    return 0;
}
void showmovies(Item &item)
{
        std::cout << "Movie: " << item.title << "  Rating: "
             << item.rating << std::endl;
}

上面的代码刚刚编译并成功运行。有人能告诉我为什么函数showmovies()可以使用引用访问simplist的项成员，而不被声明为友元函数或成员函数吗？