c++ dynamic array initialization crash

Question

I have the following code where i call a function and create a dynamic array of ints and then fill that array with an algorithm

main.cpp

...
int main(void){

    srand((long) 1234567);

    callFunction1();

    return 0;

}

functions.h

...
    int *A;
    int N;

    //prototype
    void callFunction2();

    void callFunction1(){

         int choice;
         cin >> choice;

         while (choice != 2){

               callFunction2();

               cin >> choice;
         }

    }

    void callFunction2(){

         cout << "Enter array size" << endl;
         cin >> N;

         A = new int[N];
         A[0] = 0;
         A[1] = 1;

         for (int i=2;i<=N;i++){
             A[i] = A[i-1] + A[i-2];
         }

    }

So the above code will work most of the time but some times it will crash on the line where i initialize the array

A = new int[N];

What could be the cause of this problem?

You either enter a number for N that is less or equal 1, or you enter a number for N that is so large that allocating the array would consume more than the memory available (mind possible memory fragmentation, too). — user2819245
– user2819245, Commented Oct 20, 2013 at 16:04

juanchopanza · Accepted Answer · 2013-10-20 16:01:59Z

4

You are accessing A out of bounds here:

for (int i=2;i<=N;i++){
         A[i] = ....

A can only be indexed from 0 up to N-1, i.e. in the range [0, N).

answered Oct 20, 2013 at 16:01

juanchopanza

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3 Comments

stergosz Over a year ago

Thats what i was given... Αi = Ai-1 + Ai-2 for i = 2…n

juanchopanza Over a year ago

@fxuser And that is wrong and may cause a segmentation violation. So fix it. You have to make a distinction between the expression you just posted and the indices of an array.

juanchopanza Over a year ago

@fxuser it would make more sense to change the condition of the for loop to i < N.

TheSOFan · Accepted Answer · 2013-10-20 16:05:43Z

1

You also have a memory leak in callFunction2.

answered Oct 20, 2013 at 16:05

TheSOFan

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1 Comment

stergosz Over a year ago

Because i forgot to delete the array at the end?

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