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When you try to allocate memory with new and you don't have enough space it throws exception with "bad memory allocation" in what field of it. I looked at the source code and saw that it exactly throws that exception when there's not enough space. I imagined why what field is not "Not enough memory". That way we could know why allocation failed.
I am using VS2008 SP1.
Any idea?
Using the debugger, configure it to break when an exception is thrown. The call stack will show what's going on.Quote:
Originally Posted by siavoshkc
How to: Break When an Exception is Thrown
I think he's asking why MS didn't choose a better name in their error handling, not how to trap an error.
As to why they chose the error message, I have no idea. If there's really only one possible message, then presumably they wanted to be very general about what it was.
The actual C++ exception thrown is called std::bad_alloc. So a "bad allocation" is exactly what happens.Quote:
Originally Posted by tabstop
But the implementation is allowed to put anything it wants in the .what member of that exception.Quote:
Originally Posted by brewbuck
Yes, this is what I meant.Quote:
Originally Posted by tabstop
If there is only one message, why there should be any message?Quote:
Originally Posted by tabstop
Because std::bad_alloc derives from std::exception, and therefore must implement what(). How could the message be improved?Quote:
Originally Posted by siavoshkc
Quote:
Originally Posted by brewbuck
I am forced to type something here as I cannot make a post of only quotes.Quote:
Originally Posted by siavoshkc
(And as I said above, if there's only the one message, then there may well be other points of failure that they are worried about that you missed/don't exist, so they went with a generic message.)
Kind of what I'm getting at. Even if new fails because memory couldn't be found, the message "Out of memory" may not really explain what happened adequately. It could be that some other, usually dormant, program on the system woke up momentarily, used a huge chunk of memory, then released it and went back to sleep -- "out of memory" in that case is really just an unfortunate sequence of events -- if your code had requested memory a fraction of a second later, it might have succeeded. There are so many reasons why a particular memory allocation could fail that really, all you can say is that it failed.Quote:
Originally Posted by tabstop
So it is not defined by standard and when std library implementor writes code, he/she exactly knows where and when exceptions are thrown. Thus a very clear text message on exception can be defined.Quote:
Originally Posted by MSDN
If this is such a big deal for you, do the work.
You only need to: create a class derived from `std::bad_alloc'; replace the current allocation handler; decide on a limiting factor for retries; provide an API to set and get the current limiting factor; determine a way distinguish between application errors, library errors, system error, user errors, temporarily unavailable resources, permanently unavailable resources, and attempts to obtain the resource reaching the currently set limiting factor; provide a context sensitive string representing all the relevant conditions.
Of course, this is just off the top of my head. I'm sure others could probably add to the requirements.
Enjoy.
Soma
I don't see why it matters what the error message is?
If you catch a std::bad_alloc, your new failed, end of story. You can either, give up, try again or ask for a smaller amount of memory.