Array and Pointers - runtime error

Question

I wrote a program for my assignment that involves pointers and dynamic allocation for an array, I am getting a runtime error and the program crashes, there are no compiling errors. Here is the program :

array.h :

#include <iostream>

using namespace std;

void readArray(float*, int &);
void PrintArray(float*, int);

array.cpp :

#include "array.h"

void readArray(float* array, int &size)
{
    array = new float[size];
    cout << endl;
    cout << "Enter the array elements, use spaces: ";
    for (int i = 0; i < size; i++)
    {
        cin >> array[i];
    }
    cout << endl;
}

void PrintArray(float * array, int size)
{
    for (int i = 0; i < size; i++)
    {
        cout << array[i] << " ";
    }
    cout << endl;
}

main.cpp :

#include "array.h"
int main()
{
    int size = 0;
    cout << "How many elements would you like to enter? ";
    cin >> size;
    cout << endl;
    float *array = NULL;
    readArray(array,size);
    cout << "The array size is " << size << endl;
    PrintArray(array, size);
    return 0;
}

Sample Output :

How many elements would you like to enter? 3
Enter the array elements, use spaces: 4.0 5.0 6.0
The array size is 3

Crashes here

Can someone let me know what the problem is with the PrintArray function?

songyuanyao · Accepted Answer · 2014-04-06 00:21:29Z

2

The parameter array of readArray() is passed by value, so array in main() remains NULL even if you changed it in readArray(). To make it be passed by reference. In addition, size doesn't need be passed by reference.

change

void readArray(float* array, int &size)

to

void readArray(float*& array, int size)

edited Apr 6, 2014 at 0:21

answered Apr 6, 2014 at 0:10

songyuanyao

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Comments

paulsm4 · Accepted Answer · 2014-04-06 00:15:42Z

Q: Can someone let me know what the problem is with the PrintArray function?

A: Your PrintArray function is fine.

The problem is that you never pass the array you've allocated outside of readArray.

BETTER:

float * 
readArray(int size)
{
    float* array = new float[size];
    cout << endl;
    cout << "Enter the array elements, use spaces: ";
    for (int i = 0; i < size; i++)
    {
        cin >> array[i];
    }
    cout << endl;
    return array;
}


int main()
   ...
   float *array = readArray(size);
   ...

NOTES:

If you declared a prototype for readArray() in array.h, you'll need to update it.
There are many ways to accomplish this, but the basic problem is you need ** (a pointer to a pointer) instead of * if you allocate your array inside the function. I believe passing the array pointer back as a function return is arguably the cleanest solution.

IMHO...

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