Pass a dynamic array of objects to function

Question

I am in the process of learning c++. So i know a method by which you send something to function and then work as if it was call by value but actually it is call by reference. For example

void myFUNC(string& x)

Now, I have a dynamically created array of objects. I want to pass the array to function like a method above. Here's the code snippets

City *p = new City[number]; // pointer to dynamic array of class objects

//function prototype
void list_cities(int number, City p[]){
    for(int i=0; i<number; i++){
        cout<<p[i].get_name()<<endl;
    }
}

Solution 1

Arrays are by default converted to pointers, which are then passed as reference. So, there is no provision for explicitly passing arrays by reference. That is,

void list_cities(int number, City &p[])

is not p[] being passed as reference, but makes p[] an array of references.

Code:

void list_cities(int number, City p[])
{
    for(int i=0; i<number; i++)
    {
        cout<<p[i].get_name()<<endl;
    }
}

int main()
{
    City *p = new City[number];
    list_cities(number,p);
    delete[] p;
}

Solution 2

Confusingly, a function parameter that looks like an array City p[] is actually a pointer, equivalent to City * p. So you can just pass a pointer to your dynamic array:

list_cities(number, p);

That said, prefer friendly types like std::vector<City> so you don't have to juggle pointers and carefully avoid memory leaks and worse.

Solution 3

Using std::vector you can also do the following:

void list_cities(std::vector<City> &cities)
{
    for (size_t iCity = 0; iCity < cities.size(); iCity++){
        cout << cities[iCity].get_name() << endl;
    }
}

std::vector<City> cities;
// fill list here
list_cities(cities);