[asterisk-dev] reasoning behind char[0]

[Boehm, Matthew]

Hello gents,

I've been trying to understand some of the concepts in linkedlist.h and
loader.c.  My first quandry revolves around the use of "char
resource[0]" in loader.c, struct ast_module.

 

In writing my own code examples to understand, I found this along with
ast_module -> entry -> next to be most troublesome. Nowhere in the code,
do I find were ->next is set to null, thus preventing AST_LIST_TRAVERSE
from accessing random memory space. In my code, I always segFaulted on
the first iteration over the list (containing 1 entry) because the for
loop tried to access a ->next that didn't exist because it wasn't set to
NULL.

 

So I change the behavior of AST_LIST_INSERT_TAIL to, upon !head->first
to set the .next = NULL. While this worked, this caused a strange
behavior in the value of resource[0] being truncated or just not set
correctly.

 

So I was stuck. Not setting .next to NULL allowed resource[] to maintain
its values but seg'd on any traversing of the list. Setting .next to
NULL allowed for traversing of the list but put garbled data into the
values of resource[].

 

My only fix was to change resource[0] to char *resource and do an
ast_calloc on strlen(resource_in) right before the strcpy in
load_dynamic_module().

 

I am now able to have .next = NULL which keeps my traversals sane and
preserves my values of "resource".

 

Comments?

 

-Matthew

 

Matthew Boehm,

Senior MySQL DBA, The Planet

E: mboehm at theplanet.com

C: 832-253-8258

O: 281-714-4018

Certified MySQL 5.0 DBA, #226735534

Certified MySQL Cluster 5.1 DBA, #227094842

RedHat Certified Engineer, #805009324738628

 

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