Difference Between new, delete and malloc, free in C/C++

new/ delete

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.

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

Here is an example of new/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

Here is the 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

malloc/ free

The function malloc() is used to allocate the requested size of bytes and it returns a pointer to the first byte of allocated memory. It returns null pointer, if fails.

The function free() is used to deallocate the allocated memory by malloc(). It does not change the value of pointer which means it still points the same memory location.

Here is an example of malloc/free in C language,

Example

 Live Demo

#include <stdio.h>
#include <stdlib.h>
int main() {
   int n = 4, i, *p, s = 0;
   p = (int*) malloc(n * sizeof(int));

   if(p == NULL) {
      printf("\nError! memory not allocated.");
      exit(0);
   }

   printf("\nEnter elements of array : ");

   for(i = 0; i < n; ++i) {
      scanf("%d", p + i);
      s += *(p + i);
   }
   printf("\nSum : %d", s);
   free(p);

   return 0;
}

Output

Here is the output −

Enter elements of array : 32 23 21 8
Sum : 84