After completing the basics of C++ programming, if you have stepped into the Dynamic Memory Allocation, then you might have been welcomed with “Double Free or Corruption C++ Runtime Error”.
This is a very strange error in C++ where the program gets instantly stopped if you have made any mistake with the C++ Dynamic Memory Allocation. However, the error is not as intimidating as it looks.
If you need expert guidance while understanding the error, feel free to explore our CPP assignment help services to get expert assistance.
In this article, we will first clarify the “Double Free or Corruption” C++ Error and its common reasons. Later, we will talk about some fixing methods to deal with such issues. So, let us start our discussion.
TL;DR: “Double Free Or Corruption” C++ Runtime Error
Aspect | Summary |
Definition | “Double Free Or Corruption” occurs when a dynamically allocated memory is freed twice or when accessing memory incorrectly (like out-of-bounds array access). |
Common Causes | Deleting the same pointer twice, deleting stack memory instead of heap memory, writing an array out of bounds (corruption), and using uninitialized pointers. |
Fixing Methods |
|
Real Example | A real C Problem Statement has been taken with the where pointers are initialized before use, deleted only once, and reset pointers to Nullptr after deletion. |
What Is The “Double Free Or Corruption” Error In C++?
After creating a dynamic memory, it is the primary duty of every programmer to delete or free the memory after it has been used. But if the memory is freed twice, then the “Double Free” Runtime Error happens in C++.
Also, while working with Dynamic Arrays, if you try to access any memory beyond the array range, then the same error message will come. This will not be called the “Double Free”, but the “Corruption” Error in C++.
#include <iostream>
using namespace std;
int main()
{
int* zap = new int(10);
delete zap; // First Deletion Of Pointer
delete zap; // Second Deletion Of Pointer
return 0;
}
In the above code, the “Zap” pointer is deleted twice, which will cause the “Double Free Or Corruption” runtime error. And you will face the following message as the output during compilation.
What Are The Reasons Behind the "Double Free Or Corruption" Error?
Now, after getting the meaning of the “Double Free or Corruption” Runtime Error Message, it is time to explore the potential reasons behind getting such a message in the output screen.
In this section, we will tell you the common causes for which you might get such messages on screen.
1. Deleting Same Memory:
While using Dynamic Memory, if you are trying to delete or free a deleted pointer, then such an error message can come as you are trying to delete an address that is not present in memory.
#include <iostream>
using namespace std;
int main()
{
int* ptr = new int(5);
delete ptr; // First Deletion Of Pointer
delete ptr; // Second Deletion Of Pointer
return 0;
}
In the above code, we have already deleted the PTR pointer the first time. But, still, we try to delete it a second time. For that, we will get the “Double Free or Corruption” Runtime Error.
2. Deleting Stack Memory:
Any normal variable in C++ gets stored in the Stack Memory. If we try to delete such variables that are stored in the stack memory, then such an error message will come. We can only use them in Heap Memory.
#include <iostream>
using namespace std;
int main()
{
int x = 5; // No NEW Keyword Is Used
int* ptr = &x;
delete ptr; // Deleting The Stack Pointer
return 0;
}
In the above code, no NEW Keyword is used to create the variable, so the variable is stored in the Stack Memory. As we are trying to delete the Stack Variable, a “Double Free or Corruption” Error will happen.
3. Writing Array Out Of Bounds (Corruption):
If we are trying to access any array out of its bounds or range, then we will get the “Double Free or Corruption” Runtime Error. However, this will mainly happen due to the Corruption of the Array Memory.
#include <iostream>
using namespace std;
int main()
{
int* arr = new int[2];
arr[3] = 100; // Going Beyond The Array Index
return 0;
}
How To Solve C++ “Double Free Or Corruption” Runtime Error?
As the common causes of the “Double Free Or Corruption” Error have been made clear to us, we can proceed to some effective methods for addressing the issue. In this section, we are going to tell you about them.
If you use these methods during program development, you will not face such issues in your code.
Method 1: Use NULL Pointer After Deletion
After deletion of any Dynamic Pointer, you have to reset the pointer to NULL. In this way, if you have mistakenly deleted it twice, then no error will happen in the code, and it will not be terminated.
#include <iostream>
using namespace std;
int main() {
int* ptr = new int(10);
delete ptr; // First Deletion Of Pointer
cout << "First Pointer Delete" << endl;
ptr = nullptr; // Assigning Null Pointer
delete ptr; // Second Deletion Of Pointer
cout << "Second Pointer Delete: No Error Will Happen";
return 0;
}
Explanation Of The Program:
- The pointer PTR is created with an initial value of 10. Now, we have performed our first deletion.
- Then, we are assigning the NULL Pointer to it and doing the second deletion.
- This time, no problem will happen with the deletion.
Output:
Method 2: Use Matching Allocation And Deallocation
While working with Dynamic Memory Allocation, you have to use matching Allocation and Deallocation Methods. If there is any mismatch, then you can face such a problem in your code.
#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
// If NEW Used, Then DELETE Will Be Used
int* singlePtr = new int;
delete singlePtr;
// If NEW[] Used, Then DELETE[] Will Be Used
int* arrayPtr = new int[5];
delete[] arrayPtr;
// If MALLOC() Used, Then FREE() Will Be Used
int* mallocPtr = (int*)malloc(3 * sizeof(int));
free(mallocPtr);
}
Explanation Of The Program:
- If you are using NEW, then the DELETE should be used.
- If you are using NEW[], then the DELETE[] should be used.
- And if you are using MALLOC(), then the FREE() Keyword should have been used.
Real Example: Fixing “Double Free Or Corruption” Runtime Error In C++
We hope that whatever we have discussed till now will be enough to clear your understanding about this topic. However, if you still have any doubts about fixing the error, then you have to refer to this section.
In this section, we will take a real problem statement and solve the runtime error live. So, let us check that.
Problem Statement: Write a C++ program to show the addition of any two values using pointers.
Wrong Code:
Here, we will show you the faulty code developed by a student where such an error is happening.
#include <iostream>
using namespace std;
int main()
{
int *zap = new int(10);
int *one = new int(20);
int* sum; // The Uninitialized Pointer
*sum = *zap + *one; // Adding The Values
cout << "Result Is: " << *sum << endl;
// Deleting The Pointers
free zap;
free one;
free sum;
return 0;
}
Here, the code is giving an error for the following reasons. Let us check them out.
- The SUM pointer is uninitialized, and we are performing operations on it, which is illegal.
- To delete the pointers after use, we are using FREE, which does not go with the NEW keyword.
Correct Code:
Now, we will show the correct version, which will not cause any “Double Free or Corruption” Error.
#include <iostream>
using namespace std;
int main()
{
int *zap = new int(10);
int *one = new int(20);
int* sum = new int; // The Initialized Pointer
*sum = *zap + *one; // Adding The Values
cout << "Result Is: " << *sum << endl;
// Deleting And Resetting The Pointers
delete zap;
zap = nullptr;
delete one;
one = nullptr;
delete sum;
sum = nullptr;
return 0;
}
Now, let us check out the fixing methods that are used in this code to make it perfect.
- The SUM pointer has now been initialized with the NEW Keyword.
- As the NEW Keyword is used to create the pointers, the DELETE keyword is used to free them.
- We are also resetting the deleted pointers by assigning the NULL Value to them.
Key Takeaways:
- “Double Free Or Corruption” happens when we try to delete a pointer which is already been deleted.
- If we are trying to access any array out of its index, then such a problem can arise.
- If we try to delete a variable with Stack Memory, then such an error can be seen.
- We have to use NullPtr, Smart Pointers, and Matching Deallocation to avoid such mistakes.
