PRB: Operator New Doesn't Throw bad_alloc Exception on Failure

• The C Run-time (CRT) included with: - Microsoft Visual C++, 32-bit Editions, version 5.0

SYMPTOMS

Operator new does not throw a bad_alloc exception when it fails. It simply returns a null pointer.

RESOLUTION

Operator new does call the new handler function after it fails to procure the requestion block of memory, but before it returns the null pointer. An application could install a new handler to throw a bad_alloc exception as follows:

   #include <new>
   #include <new.h>
   int my_new_handler(size_t) {
      throw std::bad_alloc();
      return 0;
   }
   int main () {
      _PNH _old_new_handler;
      _old_new_handler = _set_new_handler(my_new_handler);
      /* ... application processing ... */
      _set_new_handler(_old_new_handler);
      return 0;
   }

To install the new handler before your global objects are initialized, create a class that sets the new handler in its constructor and installs the old new handler in its destructor. Create a global object of that type and use the init_seg pragma to force this global object to be initialized before any of your global objects. The example below demonstrates this. It also demonstrates the use of _set_new_mode to cause a failed malloc call to generate an exception. Note that to do this, the code below must reside in its own source file. You cannot change the initializations segment more than once per translation unit (source file) with the pragma init_seg.

   #include <new>
   #include <new.h>
   #pragma init_seg(lib)
   int my_new_handler(size_t) {
   throw std::bad_alloc();
   return 0;
   }
   struct my_new_handler_obj{
   _PNH _old_new_handler;
   int _old_new_mode;
   _tag_g_new_handler_obj() {
      _old_new_mode = _set_new_mode(1);
      _old_new_handler = _set_new_handler(my_new_handler);
   }
   ~_tag_g_new_handler_obj() {
      _set_new_handler(_old_new_handler);
      _set_new_mode(_old_new_mode);
   }

   } _g_new_handler_obj;

   void *__cdecl operator new(size_t cb, const std::nothrow_t&) throw()
   {
    char *p;
    try {
        p = new char[cb];
    }
    catch (std::bad_alloc) {
        p = 0;
    }
    return p;
   }

STATUS

This behavior is by design though not in conformance with the ANSI Draft Working Papers for C++.

REFERENCES

For additional information, please see the following articles in the Visual C++ 5.0 online Help: