[PATCH] Add __cow_string C string constructor

[Jonathan Wakely]

On Sun, 7 Jan 2024 at 12:57, François Dumont <frs.dumont@gmail.com> wrote:
>
> Hi
>
> While working on the patch to use the cxx11 abi in gnu version namespace
> mode I got a small problem with this missing constructor. I'm not sure
> that the main patch will be integrated in gcc 14 so I think it is better
> if I propose this patch independently.
>
>      libstdc++: Add __cow_string constructor from C string
>
>      The __cow_string is instantiated from a C string in
> cow-stdexcept.cc. At the moment
>      the constructor from std::string is being used with the drawback of
> an intermediate
>      potential allocation/deallocation and copy. With the C string
> constructor we bypass
>      all those operations.

But in that file, the std::string is the COW string, which means that
when we construct a std::string and copy it, it's cheap. It's just a
reference count increment/decrement. There should be no additional
allocation or deallocation.

Am I missing something?


>
>      libstdc++-v3/ChangeLog:
>
>              * include/std/stdexcept (__cow_string(const char*)): New
> definition.
>              * src/c++11/cow-stdexcept.cc (__cow_string(const char*)):
> New definition and
>              declaration.
>
> Tested under Linux x64, ok to commit ?
>
> François
>