delete() in C++ - GeeksforGeeks

Delete is an operator that is used to destroy array and non-array(pointer) objects which are created by new expression.

Delete can be used by either using Delete operator or Delete [ ] operator
New operator is used for dynamic memory allocation which puts variables on heap memory.
Which means Delete operator deallocates memory from heap.
Pointer to object is not destroyed, value or memory block pointed by pointer is destroyed.

Here, Below are examples where we can apply delete operator:

1. Deleting Array Objects: We delete an array using [] brackets.

// Program to illustrate deletion of array 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // Allocate Heap memory 
    int* array = new int[10];  
      
    // Deallocate Heap memory 
    delete[] array;  
  
    return 0; 
} 

2. Deleting NULL pointer : Deleting a NULL does not cause any change and no error.

// C++ program to deleting 
// NULLL pointer 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // ptr is NULL pointer 
    int* ptr = NULL; 
  
    // deleting ptr 
    delete ptr; 
  
    return 0; 
} 

3. Deleting pointer with or without value

#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // Creating int pointer  
    int* ptr1 = new int;  
      
    // Initializing pointer with value 20 
    int* ptr2 = new int(20);  
  
    cout << "Value of ptr1 = " << *ptr1 << "\n"; 
    cout << "Value of ptr2 = " << *ptr2 << "\n"; 
  
    delete ptr1; // Destroying ptr1 
    delete ptr2; // Detroying ptr2 
  
    return 0; 
} 

Output:

Value of ptr1 = 0
Value of ptr2 = 20

4. Deleting a void pointer

#include <bits/stdc++.h> 
using namespace std; 
int main() 
{ 
    void* ptr; // Creating void pointer 
  
    delete ptr; // Destroying void pointer 
  
    cout << "ptr deleted successfully"; 
    return 0; 
} 

Output:

ptr deleted successfully

5. deleting memory dynamically allocated by malloc

#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // Dynamic memory allocated by using malloc 
    int* ptr2 = (int*)malloc(sizeof(int)); 
  
    delete ptr2; 
  
    cout << "ptr2 deleted successfully"; 
  
    return 0; 
} 

Output:

ptr2 deleted successfully

Although above program runs fine on GCC. It is not recommended to use delete with malloc().

6. Deleting variables of User Defined data types:

#include <bits/stdc++.h> 
using namespace std; 
  
struct P { 
    static void operator delete(void* ptr, std::size_t sz) 
    { 
        cout << "custom delete for size " << sz <<endl; 
        delete (ptr); // ::operator delete(ptr) can also be used 
    } 
    static void operator delete[](void* ptr, std::size_t sz) 
    { 
        cout << "custom delete for size " << sz <<endl; 
        delete (ptr); // ::operator delete(ptr) can also be used 
    } 
}; 
  
int main() 
{ 
    P* var1 = new P; 
    delete var1; 
  
    P* var2 = new P[10]; 
    delete[] var2; 
} 

Output:

custom delete for size 1
custom delete for size 18

Exceptions:

1. Trying to delete Non-pointer object

#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    int x; 
  
    // Delete operator always 
    // requires pointer as input 
    delete x; 
  
    return 0; 
} 

Output:

error: type ‘int’ argument given to ‘delete’, expected pointer

2. Trying to delete pointer to a local stack allocated variable.

#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    int x; 
    int* ptr1 = &x; 
  
    // x is present on stack frame as 
    // local variable, only dynamically 
    // allocated variables can be destroyed 
    // using delete operator 
    delete ptr1; 
  
    return 0; 
} 

Output:

Runtime error

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