[patch] Make vector::at() assertion message more useful

[Chris Jefferson]

On 18/08/13 08:09, Václav Zeman wrote:
> On 08/17/2013 05:10 PM, Gabriel Dos Reis wrote:
>> On Sat, Aug 17, 2013 at 5:41 AM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
>>>
>>> Hi,
>>>
>>> Paul Pluzhnikov <ppluzhnikov@google.com> ha scritto: __throw_out_of_range(__N("vector::_M_range_check"));
>>>> +        {
>>>> +          char __s[256];
>>>> +          __builtin_snprintf(__s, sizeof(__s),
>>>> +                             __N("vector::_M_range_check: %zu >= %zu"),
>>>> +                             __n, this->size());
>>>> +          __throw_out_of_range(__s);
>>>> +        }
>>> The idea makes sense, but while we are at it I think the message could be more clear, say what the two numbers are. Also, I don't think we can unconditionally call snprintf, it's C99 and supported targets lack it. Maybe with some libiberty magic? I don't think such magic automagically triggers when __builtin_snprintf is expanded, or does it? Please investigate that.
>> I agree that we can't embark a significant IO library as part of a purely
>> data structure components.
>>
>> Furthermore, __builtin_snprintf doesn't always expand to a
>> compiler magic -- it can be a normal function call.
>>
>> This would be a regression, not an improvement.
> What about adding a simple template function that converts integer into
> std::string using division by 10? You could then concatenate the message
> from std::string fragments, avoiding IO library but having to pull in
> std::string instead. Would that be acceptable?
Rather than making up new functions, why not use a std::ostringstream?

Chris