C++ New Library - operator new



It allocates size bytes of storage, suitably aligned to represent any object of that size, and returns a non-null pointer to the first byte of this block.


Following is the declaration for operator new.

void* operator new (std::size_t size) throw (std::bad_alloc);       (throwing allocation)
void* operator new (std::size_t size, const std::nothrow_t& nothrow_value) throw();                (nothrow allocation)
void* operator new (std::size_t size, void* ptr) throw();                       (placement)


  • size − It contain size in bytes of the requested memory block.

  • nothrow_value − It contains the constant nothrow.

  • ptr − It is a pointer to an already-allocated memory block of the proper size.

Return Value

It returns a pointer to the newly allocated storage space.


If it fails to allocate storage then it throws bad_alloc.

Data races

It modifies the storage referenced by the returned value.


In below example explains about new operator.

#include <iostream>
#include <new>

struct MyClass {
   int data[100];
   MyClass() {std::cout << "It constructed [" << this << "]\n";}

int main () {

   std::cout << "1: ";
   MyClass * p1 = new MyClass;

   std::cout << "2: ";
   MyClass * p2 = new (std::nothrow) MyClass;

   std::cout << "3: ";
   new (p2) MyClass;

   std::cout << "4: ";
   MyClass * p3 = (MyClass*) ::operator new (sizeof(MyClass));

   delete p1;
   delete p2;
   delete p3;

   return 0;

Let us compile and run the above program, this will produce the following result −

1: It constructed [0x21f9ba0]
2: It constructed [0x21f9d40]
3: It constructed [0x21f9d40]