Hello Pascal!

Oct 19 16:34 03, Pascal Schmidt wrote to Bo Simonsen:

 BS>>>> for(tmpStruct=firstStruct; tmpStruct;
tmpStruct=tmpStruct->next)
 BS>>>> {
 BS>>>>    free(tmpStruct);      
 BS>>>> }
 RS>>>  Well, you don't want to try to access tmpStruct after 
 RS>>> you have free'd it.  I would do something more like 
 RS>>> this...
 BS>> So you set it to NULL after freeing it?

 PS> The problem with your above code is that you do free(tmpStruct) and 
 PS> tmpStruct->then access next, but you don't know what free() does, it 
 PS> could for example overwrite the contents of tmpStruct->next. Usually 
 PS> it doesn't, but you cannot be certain.

You have a point. I just used to write linked list in that way, so I forgot
all about I needs to be written in another way for freeing..

curStruct = firstStruct;

do
{
    tmpStruct = curStruct->next;
    free(curStruct);   
    curStruct = tmpStruct;
} while(curStruct);

 PS> You could even want to have a free() that zeroes memory or writes 
 PS> some pattern to it to catch "use after free" bugs
semi-automatically. 
 PS> The Linux kernel, for example, has stuff like this in its linked list 
 PS> code. Deleting a list item writes special "poison" values into its 
 PS> prev and next pointers, so that the rest of the code can find out 
 PS> when it is being passed a list element that was supposed to be 
 PS> deleted already.

Ok.

Regards,
Bo

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