Re: Dynamic multidimensional array, deallocation of pointer not malloced..

From:

=?ISO-8859-1?Q?Erik_Wikstr=F6m?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 12 May 2007 10:09:13 GMT

Message-ID:

<dng1i.165$Tk3.239@newsb.telia.net>

On 2007-05-12 02:02, welch.ryan@gmail.com wrote:

Hi all,

Having a problem with addressing large amounts of memory. I have a
simple piece of code here that is meant to allocate a large piece of
memory on a ppc64 machine. The code is:

/*
Test to see what happens when we try to allocate a massively huge
piece of memory.
*/

#include <iostream>
#include <string>
#include <stdexcept>
using namespace std;

int main(int argc, char** argv) {
  cout << "Attemping to allocate.." << endl;

  const int ROWS = 635000;
  const int COLS = 2350;

  // Allocate.
  try {
    int** test = new int*[ROWS];
    for (int i = 0; i < ROWS; i++) {
      test[i] = new int[COLS];
      for (int j = 0; j < COLS; j++) {
        test[i][j] = 0;
      }
    }

    cout << "Allocation succeeded!" << endl;
    cout << "Press a key to deallocate and continue.." << endl;
    string blank;
    getline(cin,blank);

    // Deallocate.
    for (int k = 0; k < ROWS; k++) {
      delete[] test[k];
    }
    delete[] test;

    cout << "Deallocation completed!" << endl;
    cout << "Press a key to terminate.." << endl;
    getline(cin,blank);
  }
  catch(bad_alloc& e) {
    cout << "Allocation failed.." << endl;
  }

  return 0;
}

If I set ROWS and COLS to 5000 and 5000, it works just fine. However,
if I set ROWS to 635000 and COLS to 2350, it will give me the
following error upon deallocation:

HugeMemory.exe(29468) malloc: *** Deallocation of a pointer not
malloced: 0x20afd2000; This could be a double free(), or free() called
with the middle of an allocated block; Try setting environment
variable MallocHelp to see tools to help debug

Note that the allocation step succeeds, and that I only receive this
error after allowing the code to deallocate the array.

I have absolutely no idea, but you could try to make the code a bit more
simple by allocating everything in one large block instead:

#include <iostream>
#include <string>
#include <stdexcept>
using namespace std;

int main() {
   cout << "Attemping to allocate.." << endl;

   const int ROWS = 635000;
   const int COLS = 2350;

   // Allocate.
   try {
     int* test = new int[ROWS * COLS];
     for (int i = 0; i < ROWS * COLS; i++) {
       test[i] = 0;
     }

     cout << "Allocation succeeded!" << endl;
     cout << "Press a key to deallocate and continue.." << endl;

     string blank;
     getline(cin,blank);

     // Deallocate.
     delete[] test;

     cout << "Deallocation completed!" << endl;
     cout << "Press a key to terminate.." << endl;
     getline(cin,blank);
   }
   catch(bad_alloc& e) {
     cout << "Allocation failed.." << endl;
   }

   return 0;
}

Do you still get the same error (or some other)? If you do there's
probably something wrong with your standard library.

--
Erik Wikstr?m