Re: [PATCH] don't store temporary value returned from c_str()

[Jani Nikula <jani@nikula.org>]

On Sat, 20 Apr 2013, Vladimir.Marek@oracle.com wrote:
> From: Vladimir Marek <vlmarek@volny.cz>
>
> This is causing problems when compiled by Oracle Studio. Memory pointed
> by (const char*)term was already changed once talloc_strdup was called.
>
> Signed-off-by: Vladimir Marek <vlmarek@volny.cz>
> ---
>  lib/message.cc |    9 ++++-----
>  1 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/lib/message.cc b/lib/message.cc
> index 8720c1b..8d329d1 100644
> --- a/lib/message.cc
> +++ b/lib/message.cc
> @@ -266,18 +266,17 @@ _notmuch_message_get_term (notmuch_message_t *message,
>  			   const char *prefix)
>  {
>      int prefix_len = strlen (prefix);
> -    const char *term = NULL;
>      char *value;
>  
>      i.skip_to (prefix);
>  
> -    if (i != end)
> -	term = (*i).c_str ();

It's okay to use the result of .c_str() as long as the string object
stays in scope, and none of the non-const member functions are
called. Here, I think the problem is that TermIterator's overloaded
operator*() returns a string object within the if block's scope, and it
goes immediately out of scope. You could check this by adding

	string s = *i;

in function scope, and replacing (*i) with s in the if block. This might
also be more obvious than the presented patch, but I think the patch is
fine too.

BR,
Jani.


> +    if (i == end)
> +	return NULL;
>  
> -    if (!term || strncmp (term, prefix, prefix_len))
> +    if (strncmp ((*i).c_str(), prefix, prefix_len))
>  	return NULL;
>  
> -    value = talloc_strdup (message, term + prefix_len);
> +    value = talloc_strdup (message, (*i).c_str() + prefix_len);
>  
>  #if DEBUG_DATABASE_SANITY
>      i++;
> -- 
> 1.7.3.2
>
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