On Fri, 12 Dec 2025, 03:46 叶易安 via Std-Proposals, <
std-proposals_at_[hidden]> wrote:

> Most times we would like to know as more message as possible when an error
> occurs, such as:
> 1. which argument is invalid
> 2. stacktrace [available by
> std::set_terminate(std::stacktrace::current()...)]
>
> Currently the message in [1.] is always useless.
>

Is it though?

For example:
> (clang22): "libc++abi: terminating due to uncaught exception of type
> std::out_of_range: vector"
>
> Gcc15 saw this problem, and has internally changed the `std::vector::at()`
> implementation by calling a new `__throw_out_of_range_fmt`. Now gcc can
> provide a much helpful output:
> (gcc15): "what(): vector::_M_range_check: __n (which is 42) >=
> this->size() (which is 24)"
>

So not always useless then. It's a problem of the code throwing the
exception.


> Can we add a new overload constructor to make the exceptions-formatting in
> a standard way?
> =====
> /*new overload*/
> throw std::out_of_range("index {} is out of range with size {}", pos,
> this->size());
>
> /*currently available, but verbose | tedious! */
> throw std::out_of_range(std::format("index {} is out of range with size
> {}", pos, this->size()));
>

I'm not convinced by the motivation. Throwing exceptions isn't something
that's so common that we need to save 13 characters here. The std::format
solution seems fine.

Note that the libstdc++ helper function doesn't rely on any new
constructor, it just formats a string and passes that to the existing
constructor. You can write your own helper functions to do that too.



> /*add a new overload*/
> std::logic_error::logic_error(std::format_string<Ts...>, Ts&&...)
>

And every other exception type in <stdexcept>?


=====
>
> And:
> 1. This will not break ABI.
> 2. We **encourage** users to carry essential information, rather than a
> plain text.
>

It's already possible today though.

>