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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