Return array from a function

Question

I try to return an array from function in C++. I made a very easy function to demonstrate it.

#include<iostream>
using namespace std;

int OneDimensional();

void main()
{
    int arr[3];
    arr = OneDimensional();

    cout<<"arr = " << arr[0] <<endl;

    cin.get(); cin.get();
}

int OneDimensional()
{
    int arr[3];
    cout << "Enter a number" <<endl;
    cin  >> arr[0];
    cout << "Enter a number" <<endl;
    cin  >> arr[1];
    cout << "Enter a number" <<endl;
    cin  >> arr[2]; 
    return arr;
}

But it fails with a lot of errors.

for further reading: [What should main() return in C and C++?](http://stackoverflow.com/q/204476/3953764) — Piotr Skotnicki, Sep 24 '15 at 07:23
arr in OneDimensional allocates array on its stack and you are trying to return pointer to stack - very bad idea. Also a lot of bugs. Try read some book on C/C++ programming. — Nikolai, Sep 24 '15 at 07:27

Himanshu · Accepted Answer · 2015-09-24T07:44:32.730

0

you need to use a pointer.

int * OneDimensional()
{
    static int arr[3];
    cout << "Enter a number" <<endl;
    cin  >> arr[0];
    cout << "Enter a number" <<endl;
    cin  >> arr[1];
    cout << "Enter a number" <<endl;
    cin  >> arr[2]; 
    return arr;
}

void main()
{
    int *arr;
    arr = OneDimensional();

    for (int i = 0; i < length; i++ )// length is number of elements in array
   {
       cout<<"arr = "<< *(arr + i) << endl;
   }
}

Check the example here

edited Sep 24 '15 at 07:44

answered Sep 24 '15 at 07:27

Himanshu

4,327
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Your function returns a pointer to a local temporary. – randooom Sep 24 '15 at 07:29
you're returning a dangling pointer – Piotr Skotnicki Sep 24 '15 at 07:30
@randooom , i have used `static int arr[3];` – Himanshu Sep 24 '15 at 07:39
@PiotrSkotnicki, program is working fine I have checked. – Himanshu Sep 24 '15 at 07:40
With this method you'll get the same array each time you call `OneDimensional`. – TartanLlama Sep 24 '15 at 07:41
1

@Himanshu sure, once you have changed it to a static array, now the pointer to it won't get invalidated – Piotr Skotnicki Sep 24 '15 at 07:42
1

And you should certainly not `delete[]` an array created without `new[]`. – TartanLlama Sep 24 '15 at 07:44
@TartanLlama, yes you are right. thanks. – Himanshu Sep 24 '15 at 07:45
`cin.get()` is missing and `length` is not declared, `static`is not necessary. But other than that, it works, thx! – Black Sep 24 '15 at 07:53
@EdwardBlack, `length` you can pass according to number of array element you care using. in this program you can pass `3` in place of `length`. – Himanshu Sep 24 '15 at 07:58
1

@EdwardBlack if you don't use `static` then you'll return a dangling pointer. – TartanLlama Sep 24 '15 at 08:13
@Himanshu one last question, does this also work with multi dimensional arrays? – Black Sep 24 '15 at 08:14
@EdwardBlack Please have a look at the question which Piotr marked as a [duplicate](http://stackoverflow.com/questions/4264304/how-to-return-an-array-from-a-function), those answers are preferable to this. – TartanLlama Sep 24 '15 at 08:23
@TartanLlama sorry if the question is dumb, but what is bad about "dangling pointers". Is it creating a memory leak? – Black Sep 24 '15 at 08:34
1

@EdwardBlack dereferencing it leads to undefined behaviour. It might work today, but could crash your machine, order pizza or give you nasal demons tomorrow. – TartanLlama Sep 24 '15 at 08:35

score -2 · Answer 2 · answered Sep 24 '15 at 07:27

-2

int OneDimensional() return only a int value, not an array.
main() doesn't have a return

You need read more about C or C++.

Goold Luck!

answered Sep 24 '15 at 07:27

David Isla

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*"main() doesn't have a return"*, `main` doesn't need an explicit return statement – Piotr Skotnicki Sep 24 '15 at 07:27
Although it should be declared as returning an `int`. – TartanLlama Sep 24 '15 at 07:40
2

@David Isla, maybe you are the one who should read a C++ book, lol – Black Sep 24 '15 at 07:52
@EdwardBlack lol, yes sure! ^^ – David Isla Sep 24 '15 at 08:00

Return array from a function

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