Double free or corruption (out) and how to check whether a destructor works properly [closed]

问题

I am trying to improve my 2D array to be created using a class. All methods work fine, it is properly printed out and so on, but when I try to create a destructor I either get an error double free or corruption, I am able to get rid of the error message but then I am not sure whether the memory has been de-allocated properly, because I am using two new keywords but only one delete.

Here is my class declaration:

#pragma once    
class myPlan 
{ 
    int slots; 
    int rows = 3;
  
    int **cell; 
  
public: 
    myPlan(int slots);   // Constructor 
    ~myPlan();
};

and here is definition

#include "myPlan.hpp"

myPlan::myPlan(int slots) 
{ 
    this->slots = slots;
  
    // Create a dynamic array of pointers 
    cell = new int* [rows]; 
  
    // Create a row for every pointer 
    for (int i=0; i<slots; i++) 
    { 
       cell[i] = new int[slots];  
    } 
   for(int i =0; i<3; i++)
   {
    for (int j=0; j<slots; j++) 
    { 
       cell[i][j] = 0;  //setting all cells to zero
    }
   }

} 

//this destructor works
myPlan::~myPlan()
{

   std::cout<<"preparing for destruction"<<std::endl;
        delete[] cell;
   
   std::cout<<"Destroyed class"<<std::endl;
}

//this returns the double free error
/*
myPlan::~myPlan()
{
    for(int i = 0; i < rows; ++i)    
        {
            delete[] cell[i];
        }
        delete[] cell;
}

*/

I know that this is performance-wise slower solution (heap allocation), I tried to use std::vector way.

Thank you very much for any help

回答1:

Your constructor allocates a top-level array of size rows (3) but then goes on to fill slots (10) elements of it:

cell = new int* [rows]; 

// Create a row for every pointer 
for (int i=0; i<slots; i++) 
{ 
   cell[i] = new int[slots];  
}

As cell only holds 3 elements, the 7 allocations after firmly corrupt the heap by writing past allocated memory. If you run your code under valgrind or Memory sanitizer, this error should immediately stand out.

来源：https://stackoverflow.com/questions/64168457/double-free-or-corruption-out-and-how-to-check-whether-a-destructor-works-prop

标签

c++

arrays

oop