Simple exception question

[sfx81]

hi. I started learning exceptions just now. The following program crashes without entering catch block, I was wondering why...
Any help

	try
	{
		int *p = NULL;
		*p = 10;
	}
	catch (...)
	{
		printf("Exception occurred");
	}

[Dudester]

First off when using pointers you have to assign them to a variable say integer X not NULL. Second you are assigning the value pointed to by p a value even though p is not pointing to anything. This is probably what caused the crash.

[helios]

Actually, it's okay to assign it null or nothing at all, but it must be assigned something before being dereferenced (*p).
And yes. Writing to NULL causes a segmentation fault and the program crashes.

[sfx81]

i understand why this program crashes. I was trying to make understanding of exception. when i call *p = 10, it should pass control to catch block rather than crashing, isnt it ???

[helios]

I'm not entirely sure, but segmentation faults can't be caught. The kernel detects them and terminates the guilty program before the program can react (since it's waiting confirmation from the kernel).

[Zaita]

Technically, an exception has not occurred. You have written to invalid memory causing the application to crash. A catch is only good to catch a thrown exception.

[Duthomhas]

It is an (unfortunate, IMO) part of C++'s design philosophy.

Page faults (writing to *0, invalid memory, etc.) are purposefully not caught by a try..catch block.

If you are using VC++ (or other Win32-smart compilers) you can enable SEH integration into standard exceptions.

Otherwise you'll have to roll your own. I responded similarly not too long ago (on DaniWeb):
http://www.daniweb.com/forums/thread144854.html#post687600

Hope this helps.