Handling new allocation failure

When the new operator creates a new object, it calls the operator new() or operator new[]() function to obtain the needed storage.

When new cannot allocate storage to create a new object, it calls a new handler function if one has been installed by a call to set_new_handler(). The std::set_new_handler() function is declared in the header <new>. Use it to call a new handler you have defined or the default new handler.

Your new handler must perform one of the following:

• obtain more storage for memory allocation, then return
• throw an exception of type std::bad_alloc or a class derived from std::bad_alloc
• call either abort() or exit()

The set_new_handler() function has the prototype:

typedef void(*PNH)();
PNH set_new_handler(PNH);

set_new_handler() takes as an argument a pointer to a function (the new handler), which has no arguments and returns void. It returns a pointer to the previous new handler function.

If you do not specify your own set_new_handler() function, new throws an exception of type std::bad_alloc.

The following program fragment shows how you could use set_new_handler() to return a message if the new operator cannot allocate storage:

#include <iostream>
#include <new>
#include <cstdlib>
using namespace std;

void no_storage()
{
    std::cerr << "Operator new failed: no storage is
    available.\n";
      std::exit(1);
}
int main(void)
{
     std::set_new_handler(&no_storage);
   // Rest of program ...
}

If the program fails because new cannot allocate storage, the program exits with the message:

 Operator new failed:
no storage is available.