Re: %destructor

[Hans Aberg]

> On 26 Sep 2014, at 03:31, Bob Rossi <address@hidden> wrote:

> A secondary concern I had with %destructor is how it worked when lists
> are used in the bison grammar. I'm concerned about a double free. For
> instance,
>    result_list: {
>      $$ = NULL;
>    };
> 
>    result_list: result_list COMMA result {
>      $$ = append_gdbmi_result ($1, $3);
>    };
> 
>    result: variable {
>      $$ = gdbmi_result_alloc();
>      $$->variable = $1;
>    };
> 
>    variable: STRING_LITERAL {
>      char *text = gdbmi_get_text(yyscanner);
>      $$ = strdup(text);
>    };
> 
>    %destructor { gdbmi_result_free($$); } result_list
>    %destructor { gdbmi_result_free($$); } result
>    %destructor { free($$); } variable
> 
> The %destructor for result and result_list does not call free, but
> instead calls gdbmi_result_free. gdbmi_result_free free's the result
> (including the variable member of the result), and the result's next
> pointer, and so on.
> 
> Is it correct for me to call gdbmi_result_free($$) instead of free($$)?

The %destructor is for making C style cleanup during an error recovery: the 
Bison generated parser will then skip forward, bypassing any normal 
deallocations in the actions. So first write the parser in normal C style, with 
deallocators in each instance matching the allocator used in the actions. Then 
add %destructor if needed for the error recovery.