Creating a temporary array with pointers C++

Question

I was wondering if this is the proper way create a temporary array using pointers in a class. Part of my problem says this:

getMedian – returns the median value of the array. See Chapter 10 Programming Challenge 6 (p. 693) for a discussion of the term median. Taking the median will require a sorted array. You will need to create a temporary array to sort the values (to preserve the ordering of numbers). Do not sort the private member numbers array. Dynamically allocate/deallocate a temporary array in your getMedian function to determine the median.

My code:

double Statistics::getMedian() const
{
    int tempArray[length];

    for (int k = 0; k < length; k++){
        tempArray[k] = numbers[k];
    }

    bubbleSort(tempArray);

    return 0;
}

Before obviously doing the median part and a proper return statement, is this.

How you properly copy over a temporary array to alter for this problem? I don't think it is because I'm not properly allocating or deallocating anything, but I don't understand how to create a temporary array without altering the original.

if length is not a compile time constant, then you use Variable Length Array extension, and is not valid C++. — Jarod42
– Jarod42, Commented Apr 8, 2016 at 23:07
@Jarod42 Which is not such of a big deal unless you are using MSVC. — AnArrayOfFunctions
– AnArrayOfFunctions, Commented Apr 8, 2016 at 23:18
@FISOCPP you should see what that extension can do to your code size in an embedded system. And you should see what it does to the behaviour of the sizeof operator. — user4581301
– user4581301, Commented Apr 8, 2016 at 23:30
@user4581301 I know those things pretty well and I still prefer it. — AnArrayOfFunctions
– AnArrayOfFunctions, Commented Apr 9, 2016 at 1:33

Community · Accepted Answer · 2017-05-23 12:15:53Z

0

Your assignment says you are to allocate/deallocate the array dynamically. That means (in C++) using new and delete. Since you want an array, you should use array space allocator operators new[] and delete[].

double Statistics::getMedian() const
{
    int *tempArray = new int[length];

    for (int k = 0; k < length; k++){
        tempArray[k] = numbers[k];
    }

    // work with tempArray

    delete[] tempArray;

    return 0;  // or the median
}

EDIT: As suggested in the comment below, modern (C++11 and newer) way is to use smart pointers. That would mean your code could look like this.

#include <memory>

double Statistics::getMedian() const
{
    std::unique_ptr<int[]> tempArray (new int[length]);

    for (int k = 0; k < length; k++){
        tempArray[k] = numbers[k];
    }

    // work with tempArray like you would with an old pointer

    return 0;  // or the median
    // no delete[], the array will deallocate automatically
}

Check unique_ptr template class for more details. Note that this solution might not be what your professor wants, especially when the assignment talks about deallocation.

edited May 23, 2017 at 12:15

CommunityBot

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answered Apr 8, 2016 at 23:17

Honza Remeš

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1 Comment

user4581301 Over a year ago

Worth adding in a comment about using smart pointers to guard the pointer from unexpected departure from the function without hitting the delete.

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