CODEWITHSUNDEEP
c++arraysdynamicmultidimensional-arrayallocation
Arik
Arik

Reputation: 43

Run-time error on 2D array dynamic arrays

I have the following code:

int **arr = new int*[5];

for(int i = 0; i < 5; ++i)
    arr[i] = new int[];

for(int i = 0; i < 5; ++i)
    delete [] arr[i];

delete [] arr;

Now it compiles and runs successfully, however if I remove the array size '5' from the first line the code compiles but crashes with run-time error on the last line. I have the following questions that I have failed to find answers in Straustrup's C++ book, in the internet etc.

  1. Why the code crashes in the specified case ? (My guess is that delete [] fails to find the array size to be deleted and crashes.)
  2. If it is not allowed to allocate multidimensional arrays without indicating the size why such errors are not caught by compiler at compile time ?

Upvotes: 4

Views: 689

Answers (1)

Seth Carnegie
Seth Carnegie

Reputation: 75150

With the [5], you're getting an array of 5 int*s.

If you remove the [5], you're saying you want a pointer to a pointer to an int. So essentially, you have new int*[1].

Then you are indexing it with numbers from 0 to 4, which is out of bounds.

Upvotes: 3

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