3

I'm trying to design a class that needs to dynamically allocate some memory..

I had planned to allocate the memory it needs during construction, but how do I handle failed memory allocations? Should I throw an exception? I read somewhere that exceptions should only be used for "exceptional" cases, and running out of memory doesn't seem like an exceptional case to me..

Should I allocate memory in a separate initialization routine instead and check for failures and then destroy the class instance gracefully?

Or should I use exceptions instead? The class won't have anything useful to do if these memory allocations should fail..

EDIT: The consensus seems to be that running out of memory IS an exceptional case.

Will see how to go about this.. Thanks.. :)

krebstar
  • 3,956
  • 8
  • 46
  • 64

3 Answers3

15

Assuming you are using new to allocate memory, and are not overriding the new operator, it will automatically throw the std::bad_alloc exception if it fails to allocate memory properly.

I read somewhere that exceptions should only be used for "exceptional" cases, and running out of memory doesn't seem like an exceptional case to me..

Running out of memory seems like a pretty exceptional case to me :)

It is very difficult to handle this sort of situation. You may want to return a meaningful error to the user of your application, but if it's a problem caused by lack of memory, you may not even be able to afford the memory to allocate the error message. It's a bit of a catch-22 situation really.

There is a defensive programming technique (sometimes called a memory parachute or rainy day fund) where you allocate a chunk of memory when your application starts. When you then handle the bad_alloc exception, you free this memory up, and use the available memory to close down the application gracefully, including displaying a meaningful error to the user. This is much better than crashing :)

LeopardSkinPillBoxHat
  • 28,915
  • 15
  • 75
  • 111
3

I would argue that running out of memory (particularly heap memory) is an exceptional case, and if your class - and further, your application - cannot continue, I think exception throwing/handling is a very appropriate and graceful approach.

overslacked
  • 4,127
  • 24
  • 28
1

The usual behaviour in C++ when you are out of memory is to throw an exception. The built-in new operator does this by default.

Eclipse
  • 44,851
  • 20
  • 112
  • 171