On Thu, 29 May 2025 at 20:30, Nathan Myers <n...@cantrip.org> wrote:
>
> Change in V4:
> * Rename tests to string_view.cc
> * Adapt tests to cons/wchar_t directories
> * Define symbol __cpp_lib_sstream_from_string_view as 202406
> * Define symbol __glibcxx_want_sstream_from_string_view before version.h
> * Include version.h after other includes
> * No include type_traits
> * Drive-by comment moved to commit message
> * Each `explicit` on its own line
> * Run tests even when using old COW string
>
> Change in V3:
> * Comment that p2495 specifies a drive-by constraint omitted as redundant
> * Adjust whitespace to fit in 80 columns
>
> Change in V2:
> * Apply all review comments
> * Remove redundant drive-by "requires" on ctor from string allocator arg
> * Check allocators are plumbed through
Looks great now, thanks for iterating on it.
Please push to trunk (you'll probably need to rebase first, which will
have a merge conflict in bits/version.h but just regenerating it again
will resolve that).
> -- >8 --
>
> Implement PR libstdc++/119741 (P2495R3).
> Add constructors to stringbuf, stringstream, istringstream, and ostringstream,
> and a matching overload of str(sv) in each, that take anything convertible to
> a string_view in places where the existing ctors and function take a string.
> Note this change omits the constraint applied to the istringstream constructor
> from string cited as a "drive-by" in P2495R3, as we have determined it is
> redundant.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/119741
> * include/std/sstream: full implementation, really just
> decls, requires clause and plumbing.
> * include/bits/version.def, include/bits/version.h:
> new preprocessor symbol
> __cpp_lib_sstream_from_string_view.
> * testsuite/27_io/basic_stringbuf/cons/char/string_view.cc:
> New tests.
> * testsuite/27_io/basic_istringstream/cons/char/string_view.cc:
> New tests.
> * testsuite/27_io/basic_ostringstream/cons/char/string_view.cc:
> New tests.
> * testsuite/27_io/basic_stringstream/cons/char/string_view.cc:
> New tests.
> * testsuite/27_io/basic_stringbuf/cons/wchar_t/string_view.cc:
> New tests.
> * testsuite/27_io/basic_istringstream/cons/wchar_t/string_view.cc:
> New tests.
> * testsuite/27_io/basic_ostringstream/cons/wchar_t/string_view.cc:
> New tests.
> * testsuite/27_io/basic_stringstream/cons/wchar_t/string_view.cc:
> New tests.
> ---
> libstdc++-v3/include/bits/version.def | 11 +-
> libstdc++-v3/include/bits/version.h | 10 +
> libstdc++-v3/include/std/sstream | 198 +++++++++++++++--
> .../cons/char/string_view.cc | 195 +++++++++++++++++
> .../cons/wchar_t/string_view.cc | 3 +
> .../cons/char/string_view.cc | 194 +++++++++++++++++
> .../cons/wchar_t/string_view.cc | 3 +
> .../basic_stringbuf/cons/char/string_view.cc | 205 ++++++++++++++++++
> .../cons/wchar_t/string_view.cc | 3 +
> .../cons/char/string_view.cc | 204 +++++++++++++++++
> .../cons/wchar_t/string_view.cc | 3 +
> 11 files changed, 1010 insertions(+), 19 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_istringstream/cons/char/string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/char/string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/wchar_t/string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/char/string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/wchar_t/string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_stringstream/cons/char/string_view.cc
> create mode 100644
> libstdc++-v3/testsuite/27_io/basic_stringstream/cons/wchar_t/string_view.cc
>
> diff --git a/libstdc++-v3/include/bits/version.def
> b/libstdc++-v3/include/bits/version.def
> index 282667eabda..53bf72d95c2 100644
> --- a/libstdc++-v3/include/bits/version.def
> +++ b/libstdc++-v3/include/bits/version.def
> @@ -649,7 +649,7 @@ ftms = {
> };
> values = {
> v = 1;
> - /* For when there's no gthread. */
> + // For when there is no gthread.
> cxxmin = 17;
> hosted = yes;
> gthread = no;
> @@ -1945,6 +1945,15 @@ ftms = {
> };
> };
>
> +ftms = {
> + name = sstream_from_string_view;
> + values = {
> + v = 202306;
> + cxxmin = 26;
> + hosted = yes;
> + };
> +};
> +
> // Standard test specifications.
> stds[97] = ">= 199711L";
> stds[03] = ">= 199711L";
> diff --git a/libstdc++-v3/include/bits/version.h
> b/libstdc++-v3/include/bits/version.h
> index bb7c0479c72..0b932183e5b 100644
> --- a/libstdc++-v3/include/bits/version.h
> +++ b/libstdc++-v3/include/bits/version.h
> @@ -2174,4 +2174,14 @@
> #endif /* !defined(__cpp_lib_modules) && defined(__glibcxx_want_modules) */
> #undef __glibcxx_want_modules
>
> +#if !defined(__cpp_lib_sstream_from_string_view)
> +# if (__cplusplus >= 202306L) && _GLIBCXX_HOSTED
> +# define __glibcxx_sstream_from_string_view 202306L
> +# if defined(__glibcxx_want_all) ||
> defined(__glibcxx_want_sstream_from_string_view)
> +# define __cpp_lib_sstream_from_string_view 202306L
> +# endif
> +# endif
> +#endif /* !defined(__cpp_lib_sstream_from_string_view) &&
> defined(__glibcxx_want_sstream_from_string_view) */
> +#undef __glibcxx_want_sstream_from_string_view
> +
> #undef __glibcxx_want_all
> diff --git a/libstdc++-v3/include/std/sstream
> b/libstdc++-v3/include/std/sstream
> index ad0c16a91e8..edef599bd6f 100644
> --- a/libstdc++-v3/include/std/sstream
> +++ b/libstdc++-v3/include/std/sstream
> @@ -41,8 +41,12 @@
>
> #include <istream>
> #include <ostream>
> +
> #include <bits/alloc_traits.h> // allocator_traits, __allocator_like
>
> +#define __glibcxx_want_sstream_from_string_view
> +#include <bits/version.h>
> +
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> # define _GLIBCXX_LVAL_REF_QUAL &
> # define _GLIBCXX_SSTREAM_ALWAYS_INLINE
> @@ -52,8 +56,6 @@
> # define _GLIBCXX_SSTREAM_ALWAYS_INLINE [[__gnu__::__always_inline__]]
> #endif
>
> -
> -
> namespace std _GLIBCXX_VISIBILITY(default)
> {
> _GLIBCXX_BEGIN_NAMESPACE_VERSION
> @@ -159,6 +161,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> { __rhs._M_sync(const_cast<char_type*>(__rhs._M_string.data()), 0, 0);
> }
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> + // P0408 Efficient access to basic_stringbuf buffer
> explicit
> basic_stringbuf(const allocator_type& __a)
> : basic_stringbuf(ios_base::in | std::ios_base::out, __a)
> @@ -197,7 +200,36 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> | ios_base::out)
> : basic_stringbuf(__s, __mode, allocator_type{})
> { }
> +#endif
> +
> +#ifdef __cpp_lib_sstream_from_string_view
> + template<typename _Tp>
> + explicit
> + basic_stringbuf(const _Tp& __t,
> + ios_base::openmode __mode = ios_base::in | ios_base::out)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_stringbuf(__t, __mode, allocator_type{})
> + { }
> +
> + template<typename _Tp>
> + basic_stringbuf(const _Tp& __t, const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_stringbuf(__t, ios_base::in | ios_base::out, __a)
> + { }
>
> + template<typename _Tp>
> + basic_stringbuf(const _Tp& __t, ios_base::openmode __mode,
> + const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : _M_string(__t, __a)
> + { _M_stringbuf_init(__mode); }
> +#endif // C++26
> +
> +#if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> + // P0408 Efficient access to basic_stringbuf buffer
> basic_stringbuf(basic_stringbuf&& __rhs, const allocator_type& __a)
> : basic_stringbuf(std::move(__rhs), __a, __xfer_bufptrs(__rhs, this))
> { __rhs._M_sync(const_cast<char_type*>(__rhs._M_string.data()), 0, 0);
> }
> @@ -262,6 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> #if __cplusplus > 201703L
> #if _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> _GLIBCXX_NODISCARD
> basic_string<_CharT, _Traits, _SAlloc>
> @@ -317,6 +350,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> requires (!is_same_v<_SAlloc, _Alloc>)
> void
> @@ -335,6 +369,19 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> }
> #endif
>
> +#ifdef __cpp_lib_sstream_from_string_view
> + template <typename _Tp>
> + void
> + str(const _Tp& __t)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + {
> + basic_string_view<_CharT, _Traits> __sv{__t};
> + _M_string = __sv;
> + _M_stringbuf_init(_M_mode);
> + }
> +#endif // C++26
> +
> protected:
> // Common initialization code goes here.
> void
> @@ -521,6 +568,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> { }
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> + // P0408 Efficient access to basic_stringbuf buffer
> +
> // The move constructor initializes an __xfer_bufptrs temporary then
> // delegates to this constructor to performs moves during its lifetime.
> basic_stringbuf(basic_stringbuf&& __rhs, const allocator_type& __a,
> @@ -584,7 +633,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> */
> basic_istringstream()
> : __istream_type(), _M_stringbuf(ios_base::in)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Starts with an empty string buffer.
> @@ -601,7 +650,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> explicit
> basic_istringstream(ios_base::openmode __mode)
> : __istream_type(), _M_stringbuf(__mode | ios_base::in)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Starts with an existing string buffer.
> @@ -620,7 +669,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> basic_istringstream(const __string_type& __str,
> ios_base::openmode __mode = ios_base::in)
> : __istream_type(), _M_stringbuf(__str, __mode | ios_base::in)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief The destructor does nothing.
> @@ -637,9 +686,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> basic_istringstream(basic_istringstream&& __rhs)
> : __istream_type(std::move(__rhs)),
> _M_stringbuf(std::move(__rhs._M_stringbuf))
> - { __istream_type::set_rdbuf(&_M_stringbuf); }
> + { __istream_type::set_rdbuf(std::__addressof(_M_stringbuf)); }
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> + // P0408 Efficient access to basic_stringbuf buffer
> basic_istringstream(ios_base::openmode __mode, const allocator_type&
> __a)
> : __istream_type(), _M_stringbuf(__mode | ios_base::in, __a)
> { this->init(std::__addressof(_M_stringbuf)); }
> @@ -671,6 +721,32 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> { }
> #endif // C++20
>
> +#ifdef __cpp_lib_sstream_from_string_view
> + template <typename _Tp>
> + explicit
> + basic_istringstream(const _Tp& __t,
> + ios_base::openmode __mode = ios_base::in)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_istringstream(__t, __mode, allocator_type{})
> + { }
> +
> + template <typename _Tp>
> + basic_istringstream(const _Tp& __t, const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_istringstream(__t, ios_base::in, __a)
> + { }
> +
> + template <typename _Tp>
> + basic_istringstream(const _Tp& __t, ios_base::openmode __mode,
> + const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : __istream_type(), _M_stringbuf(__t, __mode | ios_base::in, __a)
> + { this->init(std::__addressof(_M_stringbuf)); }
> +#endif // C++26
> +
> // 27.8.3.2 Assign and swap:
>
> basic_istringstream&
> @@ -702,7 +778,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> _GLIBCXX_NODISCARD
> __stringbuf_type*
> rdbuf() const
> - { return const_cast<__stringbuf_type*>(&_M_stringbuf); }
> + { return
> const_cast<__stringbuf_type*>(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Copying out the string buffer.
> @@ -716,6 +792,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> #if __cplusplus > 201703L
> #if _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> _GLIBCXX_NODISCARD
> basic_string<_CharT, _Traits, _SAlloc>
> @@ -747,6 +824,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> requires (!is_same_v<_SAlloc, _Alloc>)
> void
> @@ -758,6 +836,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> str(__string_type&& __s)
> { _M_stringbuf.str(std::move(__s)); }
> #endif
> +
> +#ifdef __cpp_lib_sstream_from_string_view
> + template<typename _Tp>
> + void
> + str(const _Tp& __t)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + { _M_stringbuf.str(__t); }
> +#endif // C++26
> };
>
>
> @@ -812,7 +899,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> */
> basic_ostringstream()
> : __ostream_type(), _M_stringbuf(ios_base::out)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Starts with an empty string buffer.
> @@ -829,7 +916,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> explicit
> basic_ostringstream(ios_base::openmode __mode)
> : __ostream_type(), _M_stringbuf(__mode | ios_base::out)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Starts with an existing string buffer.
> @@ -848,7 +935,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> basic_ostringstream(const __string_type& __str,
> ios_base::openmode __mode = ios_base::out)
> : __ostream_type(), _M_stringbuf(__str, __mode | ios_base::out)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief The destructor does nothing.
> @@ -865,9 +952,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> basic_ostringstream(basic_ostringstream&& __rhs)
> : __ostream_type(std::move(__rhs)),
> _M_stringbuf(std::move(__rhs._M_stringbuf))
> - { __ostream_type::set_rdbuf(&_M_stringbuf); }
> + { __ostream_type::set_rdbuf(std::__addressof(_M_stringbuf)); }
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> + // P0408 Efficient access to basic_stringbuf buffer
> basic_ostringstream(ios_base::openmode __mode, const allocator_type&
> __a)
> : __ostream_type(), _M_stringbuf(__mode | ios_base::out, __a)
> { this->init(std::__addressof(_M_stringbuf)); }
> @@ -899,6 +987,32 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> { }
> #endif // C++20
>
> +#ifdef __cpp_lib_sstream_from_string_view
> + template <typename _Tp>
> + explicit
> + basic_ostringstream(
> + const _Tp& __t, ios_base::openmode __mode = ios_base::out)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_ostringstream(__t, __mode, allocator_type{})
> + { }
> +
> + template <typename _Tp>
> + basic_ostringstream(const _Tp& __t, const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_ostringstream(__t, ios_base::out, __a)
> + { }
> +
> + template <typename _Tp>
> + basic_ostringstream(const _Tp& __t, ios_base::openmode __mode,
> + const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : __ostream_type(), _M_stringbuf(__t, __mode | ios_base::out, __a)
> + { this->init(std::__addressof(_M_stringbuf)); }
> +#endif // C++26
> +
> // 27.8.3.2 Assign and swap:
>
> basic_ostringstream&
> @@ -930,7 +1044,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> _GLIBCXX_NODISCARD
> __stringbuf_type*
> rdbuf() const
> - { return const_cast<__stringbuf_type*>(&_M_stringbuf); }
> + { return
> const_cast<__stringbuf_type*>(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Copying out the string buffer.
> @@ -944,6 +1058,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> #if __cplusplus > 201703L
> #if _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> _GLIBCXX_NODISCARD
> basic_string<_CharT, _Traits, _SAlloc>
> @@ -975,6 +1090,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> requires (!is_same_v<_SAlloc, _Alloc>)
> void
> @@ -986,6 +1102,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> str(__string_type&& __s)
> { _M_stringbuf.str(std::move(__s)); }
> #endif
> +
> +#ifdef __cpp_lib_sstream_from_string_view
> + template<typename _Tp>
> + void
> + str(const _Tp& __t)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + { _M_stringbuf.str(__t); }
> +#endif // C++26
> };
>
>
> @@ -1040,7 +1165,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> */
> basic_stringstream()
> : __iostream_type(), _M_stringbuf(ios_base::out | ios_base::in)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Starts with an empty string buffer.
> @@ -1055,7 +1180,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> explicit
> basic_stringstream(ios_base::openmode __m)
> : __iostream_type(), _M_stringbuf(__m)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Starts with an existing string buffer.
> @@ -1072,7 +1197,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> basic_stringstream(const __string_type& __str,
> ios_base::openmode __m = ios_base::out |
> ios_base::in)
> : __iostream_type(), _M_stringbuf(__str, __m)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief The destructor does nothing.
> @@ -1089,12 +1214,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> basic_stringstream(basic_stringstream&& __rhs)
> : __iostream_type(std::move(__rhs)),
> _M_stringbuf(std::move(__rhs._M_stringbuf))
> - { __iostream_type::set_rdbuf(&_M_stringbuf); }
> + { __iostream_type::set_rdbuf(std::__addressof(_M_stringbuf)); }
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> + // P0408 Efficient access to basic_stringbuf buffer
> basic_stringstream(ios_base::openmode __mode, const allocator_type&
> __a)
> : __iostream_type(), _M_stringbuf(__mode, __a)
> - { this->init(&_M_stringbuf); }
> + { this->init(std::__addressof(_M_stringbuf)); }
>
> explicit
> basic_stringstream(__string_type&& __str,
> @@ -1125,6 +1251,31 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> { }
> #endif // C++20
>
> +#ifdef __cpp_lib_sstream_from_string_view
> + template <typename _Tp>
> + explicit
> + basic_stringstream(const _Tp& __t,
> + ios_base::openmode __mode = ios_base::in | ios_base::out)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_stringstream(__t, __mode, allocator_type{})
> + { }
> +
> + template <typename _Tp>
> + basic_stringstream(const _Tp& __t, const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + : basic_stringstream(__t, ios_base::in | ios_base::out, __a)
> + { }
> +
> + template <typename _Tp>
> + basic_stringstream(const _Tp& __t, ios_base::openmode __mode,
> + const allocator_type& __a)
> + requires (is_convertible_v<const _Tp&, basic_string_view<_CharT,
> _Traits>>)
> + : __iostream_type(), _M_stringbuf(__t, __mode, __a)
> + { this->init(std::__addressof(_M_stringbuf)); }
> +#endif // C++26
> +
> // 27.8.3.2 Assign and swap:
>
> basic_stringstream&
> @@ -1156,7 +1307,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> _GLIBCXX_NODISCARD
> __stringbuf_type*
> rdbuf() const
> - { return const_cast<__stringbuf_type*>(&_M_stringbuf); }
> + { return
> const_cast<__stringbuf_type*>(std::__addressof(_M_stringbuf)); }
>
> /**
> * @brief Copying out the string buffer.
> @@ -1170,6 +1321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> #if __cplusplus > 201703L
> #if _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> _GLIBCXX_NODISCARD
> basic_string<_CharT, _Traits, _SAlloc>
> @@ -1201,6 +1353,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
>
> #if __cplusplus > 201703L && _GLIBCXX_USE_CXX11_ABI
> #if __cpp_concepts
> + // P0407 Allocator-aware basic_streambuf
> template<__allocator_like _SAlloc>
> requires (!is_same_v<_SAlloc, _Alloc>)
> void
> @@ -1212,6 +1365,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
> str(__string_type&& __s)
> { _M_stringbuf.str(std::move(__s)); }
> #endif
> +
> +#ifdef __cpp_lib_sstream_from_string_view
> + template<typename _Tp>
> + void
> + str(const _Tp& __t)
> + requires (is_convertible_v<const _Tp&,
> + basic_string_view<_CharT, _Traits>>)
> + { _M_stringbuf.str(__t); }
> +#endif // C++26
> };
>
> #if __cplusplus >= 201103L
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/char/string_view.cc
> b/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/char/string_view.cc
> new file mode 100644
> index 00000000000..27f65aa9437
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/char/string_view.cc
> @@ -0,0 +1,195 @@
> +// C++26 [istringstream.general]
> +
> +// { dg-do run { target c++26 } }
> +
> +#include <sstream>
> +#include <string>
> +#include <string_view>
> +#include <testsuite_allocator.h>
> +#include <testsuite_hooks.h>
> +
> +// Check C++26 P2495 istringstream ctors and members str(s) that accept a
> +// string_view, or anything convertible to a string_view, in place of a
> +// string object. Mostly just verify plumbing.
> +
> +#ifndef C
> +# define C char
> +# define L(a) a
> +#endif
> +
> +using string = std::basic_string<C>;
> +using string_view = std::basic_string_view<C>;
> +using istringstream = std::basic_istringstream<C>;
> +
> +struct convertible_to_string_view {
> + string s;
> + operator string_view() const { return s; }
> +};
> +
> +const string str(L("This is a test string"));
> +convertible_to_string_view cstr{str}; // a copy
> +const convertible_to_string_view ccstr{str}; // another copy
> +
> +template <typename istringstream = std::basic_istringstream<C>>
> +void
> +test01()
> +{
> + // Test C++26 constructor and str(s) taking a generalized string_view
> +
> + static_assert(! requires { istringstream(1); },
> + "istringstream ctor should reject what cannot be converted to a
> string_view");
> + static_assert(! requires { istringstream().str(1); },
> + "istringstream::str(s) should reject what cannot be converted to a
> string_view");
> +
> + static_assert(!std::is_convertible_v<string_view, istringstream>,
> + "istringstream(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<const string_view, istringstream>,
> + "istringstream(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<convertible_to_string_view,
> istringstream>,
> + "istringstream(convertible_to_string_view, ios::openmode) is
> explicit");
> + static_assert(!std::is_convertible_v<const convertible_to_string_view,
> istringstream>,
> + "istringstream(convertible_to_string_view, ios::openmode) is
> explicit");
> +
> + {
> + istringstream istr(cstr);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + }
> + {
> + istringstream istr(ccstr);
> + VERIFY( istr.str() == ccstr.s );
> + VERIFY( istr.get() == ccstr.s[0] );
> + }
> + {
> + istringstream istr(cstr, std::ios_base::in);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') != 'X' );
> + }
> + {
> + istringstream istr(cstr, std::ios_base::out);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') == 'X' );
> + }
> +}
> +
> +void
> +test02()
> +{
> + // Test various C++26 constructors taking string views
> + // and mix of other arguments
> +
> + auto const mode = std::ios_base::in | std::ios_base::out;
> +
> + {
> + // template <typename T>
> + // basic_istringstream(const T&, ios_base::openmode, const
> allocator_type&)
> +
> + istringstream::allocator_type a;
> + {
> + istringstream istr(cstr, mode, a); // ={} checks for non-explicit ctor
> + VERIFY( istr.str() == cstr.s );
> + }
> + {
> + istringstream istr(cstr, std::ios::in, a);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') != 'X' );
> + }
> + {
> + istringstream istr(cstr, std::ios::out, a);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') == 'X' );
> + }
> + }
> +
> + {
> + // template <typename T>
> + // basic_istringstream(const T&, ios_base::openmode)
> + {
> + istringstream istr(cstr, mode);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') == 'X' );
> + }
> + {
> + istringstream istr(cstr, std::ios::in);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') != 'X' );
> + }
> + {
> + istringstream istr(cstr, std::ios::out);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') == 'X' );
> + }
> + }
> +
> + {
> + // template <typename T>
> + // explicit
> + // basic_istringstream(const T&, ios_base::openmode = ios_base::in)
> +
> + istringstream istr(cstr);
> + VERIFY( istr.str() == cstr.s );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') != 'X' );
> + }
> +}
> +
> +using alloc_type = __gnu_test::uneq_allocator<C>;
> +
> +template<typename Alloc, typename CC = typename Alloc::value_type>
> + using istringstream_with_alloc
> + = std::basic_istringstream<CC, std::char_traits<CC>, Alloc>;
> +
> +void test03()
> +{
> + alloc_type a{1};
> + {
> + istringstream_with_alloc<alloc_type> istr(cstr, a);
> + VERIFY( istr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{istr.str()} == cstr );
> + VERIFY( istr.get() == cstr.s[0] );
> + }
> + {
> + istringstream_with_alloc<alloc_type> istr(cstr, std::ios::in, a);
> + VERIFY( istr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{istr.str()} == cstr );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') != 'X' );
> + }
> + {
> + istringstream_with_alloc<alloc_type> istr(cstr, std::ios::out, a);
> + VERIFY( istr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{istr.str()} == cstr );
> + VERIFY( istr.get() == cstr.s[0] );
> + VERIFY( istr.rdbuf()->sputc('X') == 'X' );
> + }
> +}
> +
> +void test04()
> +{
> + {
> + istringstream istr;
> + istr.str( cstr );
> + VERIFY( istr.str() == cstr.s );
> + }
> + {
> + istringstream istr;
> + istr.str( ccstr );
> + VERIFY( istr.str() == ccstr.s );
> + }
> +}
> +
> +int
> +main()
> +{
> + test01();
> + test02();
> + test03();
> + test04();
> +}
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/string_view.cc
>
> b/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/string_view.cc
> new file mode 100644
> index 00000000000..cfb73c4c510
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/string_view.cc
> @@ -0,0 +1,3 @@
> +#define C wchar_t
> +#define L(a) L##a
> +#include "../char/string_view.cc"
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/char/string_view.cc
> b/libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/char/string_view.cc
> new file mode 100644
> index 00000000000..731e97e4aa2
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/char/string_view.cc
> @@ -0,0 +1,194 @@
> +// C++26 [ostringstream.general]
> +
> +// { dg-do run { target c++26 } }
> +
> +#include <sstream>
> +#include <string>
> +#include <string_view>
> +#include <testsuite_allocator.h>
> +#include <testsuite_hooks.h>
> +
> +// Check C++26 P2495 ostringstream ctors and members str(s) that accept a
> +// string_view, or anything convertible to a string_view, in place of a
> +// string object. Mostly just verify plumbing.
> +
> +#ifndef C
> +# define C char
> +# define L(a) a
> +#endif
> +
> +using string = std::basic_string<C>;
> +using string_view = std::basic_string_view<C>;
> +using ostringstream = std::basic_ostringstream<C>;
> +
> +struct convertible_to_string_view {
> + string s;
> + operator string_view() const { return s; }
> +};
> +
> +const string str(L("This is a test string"));
> +convertible_to_string_view cstr{str}; // a copy
> +const convertible_to_string_view ccstr{str}; // another copy
> +
> +template <typename ostringstream = std::basic_ostringstream<C>>
> +void
> +test01()
> +{
> + // Test C++26 constructor and str(s) taking a generalized string_view
> +
> + static_assert(! requires { ostringstream(1); },
> + "ostringstream ctor should reject what cannot be converted to a
> string_view");
> + static_assert(! requires { ostringstream().str(1); },
> + "ostringstream::str(s) should reject what cannot be converted to a
> string_view");
> +
> + static_assert(!std::is_convertible_v<string_view, ostringstream>,
> + "ostringstream(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<const string_view, ostringstream>,
> + "ostringstream(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<convertible_to_string_view,
> ostringstream>,
> + "ostringstream(convertible_to_string_view, ios::openmode) is
> explicit");
> + static_assert(!std::is_convertible_v<const convertible_to_string_view,
> ostringstream>,
> + "ostringstream(convertible_to_string_view, ios::openmode) is
> explicit");
> +
> + {
> + ostringstream ostrstr(cstr);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof() );
> + }
> + {
> + ostringstream ostrstr(ccstr);
> + VERIFY( ostrstr.str() == ccstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof() );
> + }
> + {
> + ostringstream ostrstr(cstr, std::ios_base::in);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == cstr.s[0]);
> + VERIFY( ostrstr.put('Y').rdstate() == ostrstr.goodbit );
> + }
> + {
> + ostringstream ostrstr(cstr, std::ios_base::out);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof() );
> + VERIFY( ostrstr.put('Y').rdstate() == ostrstr.goodbit );
> + }
> +}
> +
> +void
> +test02()
> +{
> + // Test plumbing of C++26 various constructors taking string views
> +
> + auto const mode = std::ios_base::in | std::ios_base::out;
> +
> + {
> + ostringstream::allocator_type a;
> + // template <typename T>
> + // basic_ostringstream(const T&, ios_base::openmode, const
> allocator_type&)
> + {
> + ostringstream ostrstr(cstr, mode, a); // ={} checks for non-explicit
> ctor
> + VERIFY( ostrstr.str() == cstr.s );
> + }
> + {
> + ostringstream ostrstr(cstr, std::ios::in, a);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == cstr.s[0]);
> + VERIFY( ostrstr.put('Y').rdstate() == ostrstr.goodbit );
> + }
> + {
> + ostringstream ostrstr(cstr, std::ios::out, a);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof()
> );
> + VERIFY( ostrstr.put('Y').rdstate() == ostrstr.goodbit );
> + }
> + }
> +
> + {
> + // template <typename T>
> + // basic_ostringstream(const T&, ios_base::openmode)
> + {
> + ostringstream ostrstr(cstr, mode);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == cstr.s[0]);
> + VERIFY( ostrstr.put('Y').good() );
> + }
> + {
> + ostringstream ostrstr(cstr, std::ios::in);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == cstr.s[0]);
> + VERIFY( ostrstr.put('X').good() );
> + }
> + {
> + ostringstream ostrstr(cstr, std::ios::out);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof()
> );
> + VERIFY( ostrstr.put('Y').rdstate() == ostrstr.goodbit );
> + }
> + }
> +
> + {
> + // template <typename T>
> + // explicit
> + // basic_ostringstream(const T&, ios_base::openmode = ios_base::out)
> +
> + ostringstream ostrstr(cstr);
> + VERIFY( ostrstr.str() == cstr.s );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof() );
> + VERIFY( ostrstr.put('Y').good() );
> + }
> +}
> +
> +using alloc_type = __gnu_test::uneq_allocator<C>;
> +
> +template<typename Alloc, typename CC = typename Alloc::value_type>
> + using ostringstream_with_alloc
> + = std::basic_ostringstream<CC, std::char_traits<CC>, Alloc>;
> +
> +void test03()
> +{
> + alloc_type a{1};
> + {
> + ostringstream_with_alloc<alloc_type> ostrstr(cstr, a);
> + VERIFY( ostrstr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{ostrstr.str()} == cstr );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof() );
> + VERIFY( ostrstr.put('X').good() );
> + }
> + {
> + ostringstream_with_alloc<alloc_type> ostrstr(cstr, std::ios::in, a);
> + VERIFY( ostrstr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{ostrstr.str()} == cstr );
> + VERIFY( ostrstr.rdbuf()->sgetc() == cstr.s[0]);
> + VERIFY( ostrstr.put('X').good() );
> + }
> + {
> + ostringstream_with_alloc<alloc_type> ostrstr(cstr, std::ios::out, a);
> + VERIFY( ostrstr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{ostrstr.str()} == cstr );
> + VERIFY( ostrstr.rdbuf()->sgetc() == ostringstream::traits_type::eof() );
> + VERIFY( ostrstr.put('Y').rdstate() == ostrstr.goodbit );
> + }
> +}
> +
> +void test04()
> +{
> + {
> + ostringstream ostrstr;
> + ostrstr.str(cstr);
> + VERIFY( ostrstr.str() == cstr.s );
> + }
> + {
> + ostringstream ostrstr;
> + ostrstr.str(ccstr);
> + VERIFY( ostrstr.str() == ccstr.s );
> + }
> +}
> +
> +int
> +main()
> +{
> + test01();
> + test02();
> + test03();
> + test04();
> +}
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/wchar_t/string_view.cc
>
> b/libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/wchar_t/string_view.cc
> new file mode 100644
> index 00000000000..cfb73c4c510
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/27_io/basic_ostringstream/cons/wchar_t/string_view.cc
> @@ -0,0 +1,3 @@
> +#define C wchar_t
> +#define L(a) L##a
> +#include "../char/string_view.cc"
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/char/string_view.cc
> b/libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/char/string_view.cc
> new file mode 100644
> index 00000000000..7843269c48f
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/char/string_view.cc
> @@ -0,0 +1,205 @@
> +// C++26 31.8.2.1 [stringbuf.general]
> +
> +// { dg-do run { target c++26 } }
> +
> +#include <sstream>
> +#include <string>
> +#include <string_view>
> +#include <testsuite_allocator.h>
> +#include <testsuite_hooks.h>
> +
> +// Check C++26 P2495 stringbuf ctors and members str(s) that accept a
> +// string_view, or anything convertible to a string_view, in place of a
> +// string object.
> +
> +#ifndef C
> +# define C char
> +# define L(a) a
> +#endif
> +
> +using string = std::basic_string<C>;
> +using string_view = std::basic_string_view<C>;
> +using stringbuf = std::basic_stringbuf<C>;
> +
> +struct convertible_to_string_view {
> + string s;
> + operator string_view() const { return s; }
> +};
> +
> +const string str(L("This is a test string"));
> +convertible_to_string_view cstr{str}; // a copy
> +const convertible_to_string_view ccstr{str}; // another copy
> +
> +template <typename stringbuf = std::basic_stringbuf<C>>
> +void
> +test01()
> +{
> + // Test C++26 constructor and str(s) taking a generalized string_view
> +
> + static_assert(! requires { stringbuf(1); },
> + "stringbuf ctor should reject what cannot be converted to a
> string_view");
> + static_assert(! requires { stringbuf().str(1); },
> + "stringbuf::str(s) should reject what cannot be converted to a
> string_view");
> +
> + static_assert(!std::is_convertible_v<string_view, stringbuf>,
> + "stringbuf(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<const string_view, stringbuf>,
> + "stringbuf(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<convertible_to_string_view,
> stringbuf>,
> + "stringbuf(convertible_to_string_view, ios::openmode) is explicit");
> + static_assert(
> + !std::is_convertible_v<const convertible_to_string_view, stringbuf>,
> + "stringbuf(convertible_to_string_view, ios::openmode) is explicit");
> +
> + {
> + stringbuf sbuf(cstr);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sgetc() == cstr.s[0] );
> + }
> + {
> + stringbuf sbuf(ccstr);
> + VERIFY( sbuf.str() == ccstr.s );
> + VERIFY( sbuf.sgetc() == ccstr.s[0] );
> + }
> + {
> + stringbuf sbuf(cstr, std::ios_base::in);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sgetc() == cstr.s[0] );
> + VERIFY( sbuf.sputc('X') == stringbuf::traits_type::eof() );
> + }
> + {
> + stringbuf sbuf(ccstr, std::ios_base::in);
> + VERIFY( sbuf.str() == ccstr.s );
> + VERIFY( sbuf.sgetc() == ccstr.s[0] );
> + VERIFY( sbuf.sputc('X') == stringbuf::traits_type::eof() );
> + }
> + {
> + stringbuf sbuf(cstr, std::ios_base::out);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sputc('Y') == 'Y' );
> + VERIFY( sbuf.sgetc() == stringbuf::traits_type::eof() );
> + }
> + {
> + stringbuf sbuf(ccstr, std::ios_base::out);
> + VERIFY( sbuf.str() == ccstr.s );
> + VERIFY( sbuf.sputc('Y') == 'Y' );
> + VERIFY( sbuf.sgetc() == stringbuf::traits_type::eof() );
> + }
> +}
> +
> +void
> +test02()
> +{
> + // Test C++26 constructors taking string views using different allocators
> +
> + auto const mode = std::ios_base::in | std::ios_base::out;
> +
> + {
> + // template <typename T>
> + // basic_stringbuf(const T&, ios_base::openmode, const allocator_type&)
> +
> + stringbuf::allocator_type a;
> + {
> + stringbuf sbuf(cstr, mode, a); // ={} checks for non-explicit ctor
> + VERIFY( sbuf.str() == cstr.s );
> + }
> + {
> + stringbuf sbuf(cstr, std::ios::in, a);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sgetc() == cstr.s[0] );
> + VERIFY( sbuf.sputc('X') == stringbuf::traits_type::eof() );
> + }
> +
> + {
> + stringbuf sbuf(cstr, std::ios::out, a);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sputc('X') == 'X' );
> + VERIFY( sbuf.sgetc() == stringbuf::traits_type::eof() );
> + }
> + }
> +
> + {
> + // template <typename T>
> + // basic_stringbuf(const T&, ios_base::openmode)
> + {
> + stringbuf sbuf(cstr, mode);
> + VERIFY( sbuf.str() == cstr.s );
> + }
> + {
> + stringbuf sbuf(cstr, std::ios::in);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sgetc() == cstr.s[0] );
> + VERIFY( sbuf.sputc('X') == stringbuf::traits_type::eof() );
> + }
> + {
> + stringbuf sbuf(cstr, std::ios::out);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sputc('X') == 'X' );
> + VERIFY( sbuf.sgetc() == stringbuf::traits_type::eof() );
> + }
> + }
> +
> + {
> + // template <typename T>
> + // explicit
> + // basic_stringbuf(const T&, ios_base::openmode =
> ios_base::in|ios_base::out)
> +
> + stringbuf sbuf(cstr);
> + VERIFY( sbuf.str() == cstr.s );
> + VERIFY( sbuf.sgetc() == cstr.s[0] );
> + }
> +}
> +
> +using alloc_type = __gnu_test::uneq_allocator<C>;
> +
> +template<typename Alloc, typename CC = typename Alloc::value_type>
> + using stringbuf_with_alloc
> + = std::basic_stringbuf<CC, std::char_traits<CC>, Alloc>;
> +
> +void test03()
> +{
> + alloc_type a{1};
> + {
> + stringbuf_with_alloc<alloc_type> sbuf(cstr, a);
> + VERIFY( sbuf.get_allocator() == a );
> + VERIFY( string_view{sbuf.str()} == cstr );
> + VERIFY( sbuf.sgetc() == cstr.s[0] );
> + }
> + {
> + stringbuf_with_alloc<alloc_type> sbuf(cstr, std::ios::in, a);
> + VERIFY( sbuf.get_allocator() == a );
> + VERIFY( string_view{sbuf.str()} == cstr );
> + VERIFY( sbuf.sgetc() == cstr.s[0] );
> + VERIFY( sbuf.sputc('X') == stringbuf::traits_type::eof() );
> + }
> + {
> + stringbuf_with_alloc<alloc_type> sbuf(cstr, std::ios::out, a);
> + VERIFY( sbuf.get_allocator() == a );
> + VERIFY( string_view{sbuf.str()} == cstr );
> + VERIFY( sbuf.sputc('X') == 'X' );
> + VERIFY( sbuf.sgetc() == stringbuf::traits_type::eof() );
> + }
> +}
> +
> +void test04()
> +{
> + {
> + stringbuf sbuf;
> + sbuf.str(cstr);
> + VERIFY( sbuf.str() == cstr.s );
> + }
> + {
> + stringbuf sbuf;
> + sbuf.str(ccstr);
> + VERIFY( sbuf.str() == ccstr.s );
> + }
> +}
> +
> +int
> +main()
> +{
> + test01();
> + test02();
> + test03();
> + test04();
> +}
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/wchar_t/string_view.cc
> b/libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/wchar_t/string_view.cc
> new file mode 100644
> index 00000000000..cfb73c4c510
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/27_io/basic_stringbuf/cons/wchar_t/string_view.cc
> @@ -0,0 +1,3 @@
> +#define C wchar_t
> +#define L(a) L##a
> +#include "../char/string_view.cc"
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/char/string_view.cc
> b/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/char/string_view.cc
> new file mode 100644
> index 00000000000..72085230442
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/char/string_view.cc
> @@ -0,0 +1,204 @@
> +// C++26 31.8.2.1 [stringstream.general]
> +
> +// { dg-do run { target c++26 } }
> +
> +#include <sstream>
> +#include <string>
> +#include <string_view>
> +#include <testsuite_allocator.h>
> +#include <testsuite_hooks.h>
> +
> +// Check C++26 P2495 stringstream ctors and members str(s) that accept a
> +// string_view, or anything convertible to a string_view, in place of a
> +// string object. Mostly just verify plumbing.
> +
> +#ifndef C
> +# define C char
> +# define L(a) a
> +#endif
> +
> +using string = std::basic_string<C>;
> +using string_view = std::basic_string_view<C>;
> +using stringstream = std::basic_stringstream<C>;
> +
> +struct convertible_to_string_view {
> + string s;
> + operator string_view() const { return s; }
> +};
> +
> +const string str(L("This is a test string"));
> +convertible_to_string_view cstr{str}; // a copy
> +const convertible_to_string_view ccstr{str}; // another copy
> +
> +template <typename stringstream = std::basic_stringstream<C>>
> +void
> +test01()
> +{
> + // Test C++26 constructor and str(s) taking a generalized string_view
> +
> + static_assert(! requires { stringstream(1); },
> + "stringstream ctor should reject what cannot be converted to a
> string_view");
> + static_assert(! requires { stringstream().str(1); },
> + "stringstream::str(s) should reject what cannot be converted to a
> string_view");
> +
> + static_assert(!std::is_convertible_v<string_view, stringstream>,
> + "stringstream(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<const string_view, stringstream>,
> + "stringstream(string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<convertible_to_string_view,
> stringstream>,
> + "stringstream(convertible_to_string_view, ios::openmode) is explicit");
> + static_assert(!std::is_convertible_v<const convertible_to_string_view,
> stringstream>,
> + "stringstream(convertible_to_string_view, ios::openmode) is explicit");
> +
> + {
> + stringstream strstr(cstr);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.get() == cstr.s[0] );
> + }
> + {
> + stringstream strstr(ccstr);
> + VERIFY( strstr.str() == ccstr.s );
> + VERIFY( strstr.get() == ccstr.s[0] );
> + }
> + {
> + stringstream strstr(cstr, std::ios_base::in);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.get() == cstr.s[0] );
> + VERIFY( strstr.put('X').rdstate() == strstr.badbit );
> + }
> + {
> + stringstream strstr(cstr, std::ios_base::out);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.put('Y').good() );
> + VERIFY( strstr.get() == stringstream::traits_type::eof());
> + }
> +}
> +
> +void
> +test02()
> +{
> + // Test C++26 various constructors taking string views
> +
> + auto const mode = std::ios_base::in | std::ios_base::out;
> +
> + {
> + // template <typename T>
> + // basic_stringstream(const T&, ios_base::openmode, const
> allocator_type&)
> +
> + stringstream::allocator_type a;
> + {
> + stringstream strstr(cstr, mode, a); // ={} checks for non-explicit ctor
> + VERIFY( strstr.str() == cstr.s );
> + }
> + {
> + stringstream strstr(cstr, std::ios::in, a);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.get() == cstr.s[0] );
> + VERIFY( strstr.put('X').rdstate() == strstr.badbit );
> + }
> + {
> + stringstream strstr(cstr, std::ios::out, a);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.put('X').good() );
> + VERIFY( strstr.get() == stringstream::traits_type::eof());
> + }
> + }
> +
> + {
> + // template <typename T>
> + // basic_stringstream(const T&, ios_base::openmode)
> +
> + {
> + stringstream strstr(cstr, mode);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.get() == cstr.s[0] );
> + VERIFY( strstr.put('X').good() );
> + }
> + {
> + stringstream strstr(cstr, std::ios::in);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.get() == cstr.s[0] );
> + VERIFY( strstr.put('X').rdstate() == strstr.badbit );
> + }
> + {
> + stringstream strstr(cstr, std::ios::out);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.put('X').good() );
> + VERIFY( strstr.get() == stringstream::traits_type::eof());
> + }
> + }
> +
> + {
> + // template <typename T>
> + // explicit
> + // basic_stringstream(const T&, ios_base::openmode =
> ios_base::in|ios_base::out)
> +
> + stringstream strstr(cstr);
> + VERIFY( strstr.str() == cstr.s );
> + VERIFY( strstr.get() == cstr.s[0] );
> + VERIFY( strstr.put('X').good() );
> + }
> +}
> +
> +// A minimal allocator with no default constructor
> +template<typename T>
> + struct NoDefaultCons : __gnu_test::SimpleAllocator<T>
> + {
> + using __gnu_test::SimpleAllocator<T>::SimpleAllocator;
> + NoDefaultCons() = delete;
> + NoDefaultCons(int) { }
> + };
> +
> +using alloc_type = __gnu_test::uneq_allocator<C>;
> +
> +template<typename Alloc, typename CC = typename Alloc::value_type>
> + using stringstream_with_alloc
> + = std::basic_stringstream<CC, std::char_traits<CC>, Alloc>;
> +
> +void test03()
> +{
> + alloc_type a{1};
> + {
> + stringstream_with_alloc<alloc_type> strstr(cstr, a);
> + VERIFY( strstr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{strstr.str()} == cstr );
> + VERIFY( strstr.get() == cstr.s[0] );
> + }
> + {
> + stringstream_with_alloc<alloc_type> strstr(cstr, std::ios::in, a);
> + VERIFY( strstr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{strstr.str()} == cstr );
> + VERIFY( strstr.get() == cstr.s[0] );
> + VERIFY( strstr.put('X').rdstate() == strstr.badbit );
> + }
> + {
> + stringstream_with_alloc<alloc_type> strstr(cstr, std::ios::out, a);
> + VERIFY( strstr.rdbuf()->get_allocator() == a );
> + VERIFY( string_view{strstr.str()} == cstr );
> + VERIFY( strstr.put('X').good() );
> + VERIFY( strstr.get() == stringstream::traits_type::eof());
> + }
> +}
> +
> +void test04()
> +{
> + {
> + stringstream strstr;
> + strstr.str( cstr );
> + VERIFY( strstr.str() == cstr.s );
> + }
> + {
> + stringstream strstr;
> + strstr.str( ccstr );
> + VERIFY( strstr.str() == ccstr.s );
> + }
> +}
> +
> +int
> +main()
> +{
> + test01();
> + test02();
> + test03();
> + test04();
> +}
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/wchar_t/string_view.cc
> b/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/wchar_t/string_view.cc
> new file mode 100644
> index 00000000000..cfb73c4c510
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/wchar_t/string_view.cc
> @@ -0,0 +1,3 @@
> +#define C wchar_t
> +#define L(a) L##a
> +#include "../char/string_view.cc"
> --
> 2.49.0
>
