Avoiding dereference of NULL pointer

[Randy Howard]

Re: Avoiding dereference of NULL pointer

On Sat, 15 Dec 2007 03:52:53 -0600, Tony Jackson wrote
(in article <slrnfm78vl.jk8 .nospam@nospam. invalid>):

Hi
>
I'm quite new to C programming - I have more of a Java background: maybe
someone here can advise me.
>
I'm nearly finishing a little program but it has some hard-to-find bugs
that basically lead to a couple pointers sometimes being NULL at the
wrong time. As it stands the program just bombs out when it tries to
dereference the NULL, which obviously isn't good (especially when it
happens with the customer looking on!!).

Rule #1: Don't show the customer the program before it is finished.

I don't think there's any serious problem to worry about,

This is almost certain to be a very poor belief to hold,

and what I'd
like to do is be able to ignore the dereference attempt and just carry
on

And this is probably not the right approach to handle it either.

- probably the next time round the loop the pointer will be OK.

Because of divine intervention?

In
Java, I'd put a try block around the main loop, and if we catch an
exception then just jump back to the start of the main loop. What's the
corresponding thing in C?

Detect the error, and take appropriate action when it occurs.


--
Randy Howard (2reply remove FOOBAR)
"The power of accurate observation is called cynicism by those
who have not got it." - George Bernard Shaw

[Eric]

Re: Avoiding dereference of NULL pointer

Randy Howard wrote:

On Sat, 15 Dec 2007 03:52:53 -0600, Tony Jackson wrote
(in article <slrnfm78vl.jk8 .nospam@nospam. invalid>):
>

>Hi
>>
>I'm quite new to C programming - I have more of a Java background: maybe
>someone here can advise me.
>>
>I'm nearly finishing a little program but it has some hard-to-find bugs
>that basically lead to a couple pointers sometimes being NULL at the
>wrong time. As it stands the program just bombs out when it tries to
>dereference the NULL, which obviously isn't good (especially when it
>happens with the customer looking on!!).

>
Rule #1: Don't show the customer the program before it is finished.
>

>I don't think there's any serious problem to worry about,

>
>
This is almost certain to be a very poor belief to hold,
>

>and what I'd
>like to do is be able to ignore the dereference attempt and just carry
>on

>
And this is probably not the right approach to handle it either.
>
- probably the next time round the loop the pointer will be OK.
>
Because of divine intervention?
>

>In
>Java, I'd put a try block around the main loop, and if we catch an
>exception then just jump back to the start of the main loop. What's the
>correspondin g thing in C?

>
Detect the error, and take appropriate action when it occurs.
>
>

Whats really scary is that guys like this might be writing aircraft control
software. Got a NULL pointer? ah dont worry, just run it 4 or 5 times it
will go. Array too small? no problemo, there's always extra space off the
end we can use. God help us! Its no wonder that most things today that have
any kind of built in control program are pure crap (e.g. remote controls,
home routers, DVR's etc etc).

[Randy Howard]

Re: Avoiding dereference of NULL pointer

On Fri, 28 Dec 2007 11:24:32 -0600, Eric wrote
(in article <LOqdnWupG6nPrO janZ2dnUVZ_sOrn Z2d@comcast.com >):

Randy Howard wrote:
>

>On Sat, 15 Dec 2007 03:52:53 -0600, Tony Jackson wrote
>(in article <slrnfm78vl.jk8 .nospam@nospam. invalid>):
>>

>>Hi
>>>
>>I'm quite new to C programming - I have more of a Java background: maybe
>>someone here can advise me.
>>>
>>I'm nearly finishing a little program but it has some hard-to-find bugs
>>that basically lead to a couple pointers sometimes being NULL at the
>>wrong time. As it stands the program just bombs out when it tries to
>>dereference the NULL, which obviously isn't good (especially when it
>>happens with the customer looking on!!).

>>
>Rule #1: Don't show the customer the program before it is finished.
>>

>>I don't think there's any serious problem to worry about,

>>
>>
>This is almost certain to be a very poor belief to hold,
>>

>>and what I'd
>>like to do is be able to ignore the dereference attempt and just carry
>>on

>>
>And this is probably not the right approach to handle it either.
>>
>- probably the next time round the loop the pointer will be OK.
>>
>Because of divine intervention?
>>

>>In
>>Java, I'd put a try block around the main loop, and if we catch an
>>exception then just jump back to the start of the main loop. What's the
>>correspondi ng thing in C?

>>
>Detect the error, and take appropriate action when it occurs.
>>
>>

Whats really scary is that guys like this might be writing aircraft control
software. Got a NULL pointer? ah dont worry, just run it 4 or 5 times it
will go.

Or a nuclear power plant, or airbag deployment code in a car, or ....
the list is quite long these days.

Array too small? no problemo, there's always extra space off the
end we can use.

Yes, and don't forget, malloc never fails. :)

God help us! Its no wonder that most things today that have
any kind of built in control program are pure crap (e.g. remote controls,
home routers, DVR's etc etc).

Yes, when everything is built by the lowest bidder, and nobody will buy
anything that's not on the top of the list, when sorted by price low to
high, then you get mostly crap.


--
Randy Howard (2reply remove FOOBAR)
"The power of accurate observation is called cynicism by those
who have not got it." - George Bernard Shaw