Question

Possible Duplicate:
C++ delete – It deletes my objects but I can still access the data?

I am curious about why I am getting the following behaviour with the following (rather contrived) code. I am using
gcc 4.4.5 on Ubuntu 10.10

#include <iostream>

int main(int argc, char *argv[])
{
  int N = 5;
  int *myarr = new int[N];//create an integer array of size 5

  for (int i = 0; i < N; ++i)
    {
      myarr[i] = 45;
      std::cout << myarr[i] << std::endl;
    }  


  delete[] myarr;//kill the memory allocated by new
  std::cout << "Let's see if the array was deleted and if we get a segfault \n" ;

  for (int i = 0; i < N; ++i)
    {
      std::cout << myarr[i] << std::endl;
    }


  return 0;
}

The code compiles even with -Wall flag on. The output is

Desktop: ./a.out
45
45
45
45
45
Let's see if the array was deleted and if we get a segfault 
0
0
45
45
45
Desktop: 

How come the myarr array can still be accessed as if it were ever deleted without a segfault?
Further even though the myarr array was deleted how come the values 45 still seem to be printed correctly in positions 2,3 and 4.

In short what is delete[] really doing here?

Answer 1

delete[] calls the destructor for each element in the array, and tells your computer that you will not use the memory any more. The memory is still there, you’re just not allowed to use it.

What you are seeing is undefined behaviour. It might fail in all sorts of ways, but because your program is so short, it will probably work as you’ve seen most of the time.