Program crashes on deleting array of pointers in struct

Question

Crashes when the delete command comes around. It's supposed make a struct with pointers to arrays, fill them with random numbers, and then deallocate the memory. Works fine until the delete command, in which it crashes with our without the for loop or boolean check.

int main() {

    cout << "start" << endl;
    //Creating Struct
    struct 
    {
        int* ptrarray[10];
        bool boolarray[10];
    } data;

    //Initializing Random Generator
    srand ( time(NULL) );
    cout << "Initializing: ";

    //Allocating Memory and generating random numbers with for loops

    for (int i = 0; i < 10; i++)
    {   
        int counter = 0; //Counts numbers set   
        cout <<  i << " "; //Counting arrays initialized    
        data.ptrarray[i] = new int [12582912]; // Memory Allocation 

        for (int j = 0; j < 12582912; j++)//Number Generating
        {
            *data.ptrarray[i] = rand() % 899 + 100;
            data.ptrarray[i]++;
            counter++;
        }

        //Checking for failed initializations and declaring if success
        if (counter == 12582912)
        {
            data.boolarray[i] = true;
        }
        else
        {
            data.boolarray[i] = false;
        }
    }

    cout << endl;

    //This is where it always crashes.
    for (int i=0; i<10; i++)
    {
        if (data.boolarray[i] == true)
            delete[] data.ptrarray[i];
    }
    cout << endl;

    return 0;
}

I'm using MS Visual studio 2010.

This formatting is terrible. Please reformat and paste in gist. — BSull
– BSull, Commented Sep 19, 2012 at 21:59

nneonneo · Accepted Answer · 2012-09-19 22:00:57Z

2

The culprit is this line:

data.ptrarray[i]++;

You are changing the pointer, then using delete [] on the modified pointer. This will not work: you must use delete[] with the exact same pointer you got from new[].

Try

data.ptrarray[i][j] = rand() % 899 + 100;

instead so you don't have to change your pointer.

answered Sep 19, 2012 at 22:00

nneonneo

181k37 gold badges331 silver badges412 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

BSull Over a year ago

Even though it's a bit slower. Unless the compiler optimizes that away.

nneonneo Over a year ago

Most modern compilers are smart enough to recognize an array-filling loop for(x=0; x<n; x++) arr[x] = f(x); and will create an appropriate temporary variable.

James P Over a year ago

Thanks a lot (and to everyone who saw the mistake). Makes perfect sense now.

James P Over a year ago

Well, okay. It deletes fine now. (I deleted data.ptrarray[i]++; and replaced *data.ptrarray[i] = rand() % 899 + 100; with data.ptrarray[i][j] = rand() % 899 + 100;) But now it doesn't print the proper range of integers, instead some wild numbers (negative, 0, way over 1000). Any ideas?

James P Over a year ago

Okay, forget that, I had to change the print function in my extended code as well. Thanks again.

user334856 · Accepted Answer · 2012-09-19 22:04:06Z

1

data.ptrarray[i]++; is the problem.

You're incrementing your reference to the data, but then not resetting it to the start before trying to delete it.

answered Sep 19, 2012 at 22:04

user334856

Comments

paxdiablo · Accepted Answer · 2012-09-19 22:10:20Z

1

Your problem lies with:

data.ptrarray[i]++;

This is modifying the pointer. When you then attempt to free that modified pointer, it crashes.

You can solve this by using a copy of the pointer to run through the array, or by indexing with thej variable as well:

data.ptrarray[i][j]

edited Sep 19, 2012 at 22:10

answered Sep 19, 2012 at 22:02

paxdiablo

888k243 gold badges1.6k silver badges2k bronze badges

Collectives™ on Stack Overflow

Program crashes on deleting array of pointers in struct

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related