Creating a global dynamically-allocted array

Question

I am new to C/C++ and I had a question about dynamically allocating arrays. Can you not make a global dynamically allocated array? What if I wanted arr to be used by multiple functions? Would I have to pass arr to every function? Basically I guess I am still confused on the concept of dynamically allocated arrays and how I could create an array that can be used by a few functions.

The following produces : error: ‘arr’ does not name a type, but I am not sure exactly why.

#include <iostream>      

using namespace std;

int * arr = NULL;
arr = new int [10];

int main() {
   arr[0] = 1;
   return 0;
}

"Global" and "dynamically allocated" are really mutually exclusive. Global variables have static storage, and dynamically allocated ones have dynamic storage. You can of course have a global pointer to a dynamically allocated object. — Kerrek SB
– Kerrek SB, Commented Feb 6, 2013 at 22:11
Oh :) well that's a typo, nit-pickers. Thanks for pointing it out, anyway :) — jrok
– jrok, Commented Feb 6, 2013 at 22:17

Eric · Accepted Answer · 2013-02-06 22:04:57Z

3

That's invalid for the same reason that this is invalid

#include <iostream>      

using namespace std;

int a = 0;
a = 2;

int main() {

}

You can't run statements outside of a function, only initializers. As a result, this works:

#include <iostream>      

using namespace std;

int *arr = new int[10];

int main() {
   arr[0] = 1;
   return 0;
}

answered Feb 6, 2013 at 22:04

Eric

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Comments

Bo Persson · Accepted Answer · 2013-02-06 22:07:28Z

3

You don't even have to make the array dynamic, you can just put the array in static memory outside main, and it will live as long as the program.

#include <iostream>     

int arr[10];

int main() {
   arr[0] = 1;
   return 0;
}

answered Feb 6, 2013 at 22:07

Bo Persson

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Comments

Aeluned · Accepted Answer · 2013-02-06 22:07:50Z

1

int* arr = new int[10];

or (since you are allocate a constant size array):

int arr[10];

answered Feb 6, 2013 at 22:07

Aeluned

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Mats Petersson · Accepted Answer · 2013-02-06 22:14:38Z

1

You can't have "code" outside of a function. You need to put the call to new inside a function - you only have one in your code: main, but as long as it is a function that is executed before you access the array, it's fine.

You can also, as the comment says, do int *arr = new int[10]; - as long as it's part of the initialization, and not on a separate line.

edited Feb 6, 2013 at 22:14

answered Feb 6, 2013 at 22:04

Mats Petersson

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1 Comment

Nik Bougalis Over a year ago

int *arr = new int[10] is perfectly valid in global scope.

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