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From: alex goldman <hello@spamm.er>
Subject: Re: memory management
Newsgroups: comp.lang.ada
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Date: Fri, 03 Jun 2005 03:12:50 -0700
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Date: 2005-06-03T03:12:50-07:00
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Steve wrote:

> struct Data_Container
> {
>     int nbValues;
>     int data[1];
> }
> 
> ...
> numElements = 100;
> struct Data_Container* dc = malloc( sizeof(Data_Container) + sizeof(int)
> *( numElements - 1));
> 
> dc->nbValues = numElements;
> for( i = 0 ; i < dc->nbValues ; i++ )
> {
>     dc->data[ i ] = 0;
> }

I think the results of doing this are undefined, according to the standard.
In fact, the section on pointer arithmetic says even something like

int* p = malloc(100*sizeof(int));

p = p + 101; // more than 1 off
p = p -  50; 
             

is allowed to lead to undefined behavior. The pointer doesn't even need to
be dereferenced! So the C standard certainly doesn't forbid bounds
checking. Why C compilers don't come with this feature as an /option/ has
always puzzled me.