new and delete operator in C++

The new operator

The new operator requests for the memory allocation in heap. If the sufficient memory is available, it initializes the memory to the pointer variable and returns its address.

Here is the syntax of new operator in C++ language,

pointer_variable = new datatype;

Here is the syntax to initialize the memory,

pointer_variable = new datatype(value);

Here is the syntax to allocate a block of memory,

pointer_variable = new datatype[size];

Here is an example of new operator in C++ language,

Example

#include <iostream>
using namespace std;
int main () {
   int *ptr1 = NULL;
   ptr1 = new int;
   float *ptr2 = new float(223.324);
   int *ptr3 = new int[28];
   *ptr1 = 28;
   cout << "Value of pointer variable 1 : " << *ptr1 << endl;
   cout << "Value of pointer variable 2 : " << *ptr2 << endl;
   if (!ptr3)
   cout << "Allocation of memory failed\n";
   else {
      for (int i = 10; i < 15; i++)
      ptr3[i] = i+1;
      cout << "Value of store in block of memory: ";
      for (int i = 10; i < 15; i++)
      cout << ptr3[i] << " ";
   }
   return 0;
}

Output

Value of pointer variable 1 : 28
Value of pointer variable 2 : 223.324
Value of store in block of memory: 11 12 13 14 15

The delete operator

The delete operator is used to deallocate the memory. User has privilege to deallocate the created pointer variable by this delete operator.

Here is the syntax of delete operator in C++ language,

delete pointer_variable;

Here is the syntax to delete the block of allocated memory,

delete[ ] pointer_variable;

Here is an example of delete operator in C++ language,

Example

 Live Demo

#include <iostream>
using namespace std;
int main () {
   int *ptr1 = NULL;
   ptr1 = new int;
   float *ptr2 = new float(299.121);
   int *ptr3 = new int[28];
   *ptr1 = 28;
   cout << "Value of pointer variable 1 : " << *ptr1 << endl;
   cout << "Value of pointer variable 2 : " << *ptr2 << endl;
   if (!ptr3)
   cout << "Allocation of memory failed\n";
   else {
      for (int i = 10; i < 15; i++)
      ptr3[i] = i+1;
      cout << "Value of store in block of memory: ";
      for (int i = 10; i < 15; i++)
      cout << ptr3[i] << " ";
   }
   delete ptr1;
   delete ptr2;
   delete[] ptr3;
   return 0;
}

Output

Value of pointer variable 1 : 28
Value of pointer variable 2 : 299.121
Value of store in block of memory: 11 12 13 14 15