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;
    }
}

How to pass the dynamic array to function like the method above — Fahad Rana
– Fahad Rana, Commented Mar 4, 2015 at 17:31
something easier? just help me out in sending the dynamic array to function — Fahad Rana
– Fahad Rana, Commented Mar 4, 2015 at 17:37
@FahadRana: What do you mean? There's nothing easier than list_cities(number, p) — Mike Seymour
– Mike Seymour, Commented Mar 4, 2015 at 17:40

Mike Seymour · Accepted Answer · 2015-03-04 17:37:53Z

3

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.

answered Mar 4, 2015 at 17:37

Mike Seymour

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Comments

shauryachats · Accepted Answer · 2017-05-11 16:33:35Z

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;
}

edited May 11, 2017 at 16:33

answered Mar 4, 2015 at 17:36

shauryachats

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1 Comment

Passer By Over a year ago

Followed a link here, arrays are not passed by reference, array to pointer conversion is performed. In this case, no array even exists, there is only a pointer.

Satara · Accepted Answer · 2015-03-04 17:48:29Z

1

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);

answered Mar 4, 2015 at 17:48

Satara

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2 Comments

Fahad Rana Over a year ago

I have no idea about vectors and they might solve but the other answers solved the problem.

Satara Over a year ago

You should definitely read about it. It's a container from the c++ Standard Template Library, which is basically a very thin wrapper around the dynamic array. But in contrast to dynamic arrays it provides basic functions e.g. for insertion or removing of elements and can handle the size of the array for you.

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