Re: bad pointer exception

From:

Victor Bazarov <v.bazarov@comcast.invalid>

Newsgroups:

comp.lang.c++

Date:

Thu, 17 Jun 2010 16:39:34 -0400

Message-ID:

<hve168$4hi$1@news.eternal-september.org>

On 6/17/2010 3:49 PM, Chris wrote:

On Jun 17, 8:08 pm, Stuart Golodetz
<sgolod...@NdOiSaPlA.pMiPpLeExA.ScEom> wrote:

Chris wrote:

Hello.

how do you catch bad pointer dereferences in C++?

example:

#include<stdio.h>
void main()
{
    try
    {
            int *pi;
            *pi = 10;
    }
    catch(...)
    {
            printf("Exception caught \n\n");
    }
}

catch handler is not executed, I get a runtime error instead.

so how?

thx
Chris

Dereferencing a bad pointer results in undefined behaviour - it doesn't
throw, so you can't catch it. You just have to make sure you don't mess
up :) If you use smart pointers (e.g. shared_ptr) instead of raw
pointers, they are sometimes checked on use (against NULL only and
generally in debug mode only), but that's about as much help as you're
likely to get. Other than that, you're pretty much on your own...

Cheers,
Stu

p.s.

1) int main()
2) #include<cstdio>
3) (Add #include<iostream> and then...) std::cout<< "Exception
caught\n\n";

"Dereferencing a bad pointer results in undefined behaviour".

How can it be undefined behaviour if it generates a runtime error time
and time again?

The definition of "undefined behaviour" is that the behaviour of the
code is not defined by the C++ language standard. Did you know we have
a standard for the language? Anyway, the Standard imposes no
requirements on the code that dereferences an uninitialized pointer.
Generating a run-time error falls under that definition - nothing in
particular is required to happen. IOW, *anything* may happen for all we
care. And it's going to be OK according to the Standard.

It's not "_random_ behaviour". It's *undefined*.

Doesn't it just mean that, when trying to access memory that isn't
yours it should be considered as 'Access violation' ?

Is there absolutely no way to prevent the program from crashing?

Please use the F1 key and read about access violations and how to deal
with them.

V
--
I do not respond to top-posted replies, please don't ask