[PATCH] libstdc++: Add Doxygen comment for string::resize_and_overwite

[Daniel Krügler]

Am Do., 23. Feb. 2023 um 18:38 Uhr schrieb Jonathan Wakely via
Libstdc++ <libstdc++@gcc.gnu.org>:
>
> Reviews of the resize_and_overwite description welcome. I've tried to
> strike a balance between pedantic precision and user-friendliness.
>
> -- >8 --
>
> This is a complicated API that should be clearly documented.
>
> Also improve the comment on basic_ios::_M_setstate.
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/basic_ios.h (basic_ios::_M_setstate): Add
>         caveat to comment.
>         * include/bits/basic_string.h (resize_and_overwrite): Add
>         doxygen comment.
> ---
>  libstdc++-v3/include/bits/basic_ios.h    |  2 +-
>  libstdc++-v3/include/bits/basic_string.h | 28 ++++++++++++++++++++++++
>  2 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/include/bits/basic_ios.h b/libstdc++-v3/include/bits/basic_ios.h
> index e0667b7d049..d0a4e7d3dfd 100644
> --- a/libstdc++-v3/include/bits/basic_ios.h
> +++ b/libstdc++-v3/include/bits/basic_ios.h
> @@ -159,7 +159,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>
>        // Flip the internal state on for the proper state bits, then
>        // rethrows the propagated exception if bit also set in
> -      // exceptions().
> +      // exceptions(). Must only be called within a catch handler.
>        void
>        _M_setstate(iostate __state)
>        {
> diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
> index c81dc0d425a..1abac655fd1 100644
> --- a/libstdc++-v3/include/bits/basic_string.h
> +++ b/libstdc++-v3/include/bits/basic_string.h
> @@ -1117,6 +1117,34 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>
>  #if __cplusplus > 202002L
>  #define __cpp_lib_string_resize_and_overwrite 202110L
> +      /** Resize the string and call a function to fill it.
> +       *
> +       * @param __n   The maximum size requested.
> +       * @param __op  A callable object that writes characters to the string.
> +       *
> +       * This is a low-level function that is easy to misuse, be careful.
> +       *
> +       * Calling `str.resize_and_overwrite(n, op)` will reserve at least `n`
> +       * characters in `str`, evaluate `n2 = std::move(op)(str.data(), n)`,
> +       * and finally set the string length to `n2` (adding a null terminator
> +       * at the end). The function object `op` is allowed to write to the
> +       * extra capacity added by the initial reserve operation, which is not
> +       * allowed if you just call `str.reserve(n)` yourself.
> +       *
> +       * This can be used to efficiently fill a `string` buffer without the
> +       * overhead of zero-initializing characters that will be overwritten
> +       * anyway.
> +       *
> +       * The callable `op` not access the string directly (only through the

Did you mean "The callable `op` <ins>must</ins> not access the string
directly" instead?

- Daniel