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

[Václav Zeman <vhaisman at gmail dot com>]

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?

-- 
VZ

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