On 12/10/2004, at 8:42 PM, Gabriel Dos Reis wrote:

> The code in build_string
>
>   memset (s, 0, sizeof (struct tree_common));
>   TREE_SET_CODE (s, STRING_CST);
>   TREE_STRING_LENGTH (s) = len;
>   memcpy ((char *) TREE_STRING_POINTER (s), str, len);
>   ((char *) TREE_STRING_POINTER (s))[len] = '\0';
>
> is trying to do similar thing, but it is undefined behaviour.
>
>        [#5] If an attempt is made to modify an object defined  with
>        a  const-qualified  type  through use of an lvalue with non-
>        const-qualified type, the  behavior  is  undefined.

The object here is '*s', which was not defined with a const-qualified 
type.  It's not defined with any type at all, it was allocated through 
malloc which is not a typed interface.  (It would be different if it 
was allocated through 'new', but we do not have new in C.)