22nd Aug - Delete Operator in C++

A delete operator is used to deallocate memory space that is dynamically created using the new operator, calloc and malloc() function, etc., at the run time of a program in C++ language. In other words, a delete operator is used to release array and non-array (pointer) objects from the heap, which the new operator dynamically allocates to put variables on heap memory. We can use either the delete operator or delete [ ] operator in our program to delete the deallocated space. A delete operator has a void return type, and hence, it does not return a value.

Syntax of delete operator

We can delete a specific element or variable using the delete operator, as shown:

delete pointer_variable; // delete ptr; It deallocates memory for one element

Similarly, we can delete the block of allocated memory space using the delete [] operator.

delete [ ] pointer_variable; // delete [] ptr; It deallocate for an array

Program to deallocate memory location of each variable using the delete operator

Let's consider an example to delete the allocated memory space of each variable from the heap memory using the delete operator.

Program1.cpp

#include <iostream> using namespace std; int main () { // declaration of variables int *ptr1, *ptr2, sum; // allocated memory space using new operator ptr1 = new int; ptr2 = new int; cout << " Enter first number: "; cin >> *ptr1; cout << " Enter second number: "; cin >> *ptr2; sum = *ptr1 + *ptr2; cout << " Sum of pointer variables = " << sum; // delete pointer variables delete ptr1; delete ptr2; return 0; }

Output

Enter first number: 5
 Enter second number: 8
 Sum of pointer variables = 13 

Program to delete the array object using the delete [] operator

Let's create a program to delete the dynamically created memory space for an array object using the delete [] operator in C++.

Program2.cpp

#include <iostream> using namespace std; int main () { // declaration of variables int *arr, max_num, i; cout << " Enter total number of elements to be entered : "; cin >>max_num; // use new operator to declare array memory at run time arr = new int [max_num]; cout << " Enter the numbers: \n"; for (i = 0; i< max_num; i++) // input array from user { cout << " Number " << i+1 << " is "; cin >> arr[i]; } cout <<" Numbers are : "; for (i = 0; i < max_num; i++) { cout << arr[i] << "\t"; } // use delete operator to deallocate dynamic memory delete [ ] arr; return 0; }

Output

Enter total number of elements to be entered : 7
 Enter the numbers:
 Number 1 is 45
 Number 2 is 600
 Number 3 is 78
 Number 4 is 93
 Number 5 is 29
 Number 6 is 128
 Number 7 is 32
 Numbers are : 45       600     78      93      29      128     32

Program to delete NULL pointer using delete operator

Let's consider a program to delete NULL pointer using the delete operator in C++ programming language.

Program3.cpp

#include <iostream> using namespace std; int main () { // initialize the integer pointer as NULL int *ptr = NULL; // delete the ptr variable delete ptr; cout << " The NULL pointer is deleted."; return 0; }

Output

The NULL pointer is deleted.

Delete a pointer with or without value using the delete operator

Let's consider an example to delete a pointer variable with or without a value using the delete operator in C++.

Program4.cpp

#include <iostream> using namespace std; int main () { // Use new operator to create dynamic memory int *ptr = new int; // Use new operator to dynamic memory space for an array int *ptr2 = new int (10); cout << " The value of ptr is: "<< *ptr << " \n "; cout << " The value of ptr2 is: "<< *ptr2 << " \n "; // use delete keyword to delete the value stored in *ptr and *ptr2 delete ptr; delete ptr2; return 0; }

Output

The value of ptr is: 1415071048
  The value of ptr2 is: 10

Program to allocate dynamic memory using the malloc function and then delete using the delete operator

Let's consider an example of creating dynamic memory using the malloc function and then using the delete operator to delete allocated memory in the C++ programming language.

Program6.cpp

#include <iostream> using namespace std; int main () { // create a dynamic memory using malloc() function char *str = (char *) malloc (sizeof (char)); cout << " Dynamic memory is deleted using the delete operator. " << endl; delete str; // use delete operator to delete the referencing pointer return 0; }

Output

Dynamic memory is deleted using the delete operator.

Program to delete variables of user defined data types

Let's write a program to demonstrate the deletion of user defined object using the delete operator.

Program7.cpp

#include <bits/stdc++.h> using namespace std; struct Ptr { static void operator delete (void *ptr1, std::size_t sz) { cout << " Custom deletion of size " << sz <<endl; delete (ptr1); // use delete() function } static void operator delete[] (void *ptr1, std:: size_t sz) { cout << " Custom deletion of size " << sz; delete (ptr1); // use ::operator delete() function } }; int main() { Ptr *data = new Ptr; // create dynamic memory delete data; // delete specific variable Ptr *data2 = new Ptr[20]; delete[] data2; // delete block of memory }

Output

Custom deletion of size 1
 Custom deletion of size 24

Program to delete a void pointer using the delete operator

Let's create a program to release the memory space of the void pointer using the delete operator in C++.

Program8.cpp

#include <iostream> using namespace std; int main () { // declare a void pointer void *str; cout << " The void pointer is deleted using the delete operator. " <<endl; // delete the void pointer reference return 0; }

Output

The void pointer is deleted using the delete operator.

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