On Wed, Jun 4, 2025 at 8:02 PM Jonathan Wakely <jwak...@redhat.com> wrote:
>
> 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).
On Fedora 42/x86-64, I got
FAIL: 27_io/basic_istringstream/cons/wchar_t/string_view.cc
-std=gnu++17 (test for excess errors)
Excess errors:
/export/gnu/import/git/gitlab/x86-gcc-test/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/../char/string_view.cc:39:
error: 'requires' only available with '-std=c++20' or '-fconcepts'
[-Wtemplate-body]
/export/gnu/import/git/gitlab/x86-gcc-test/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/../char/string_view.cc:39:
error: expected ',' before '{' token [-Wtemplate-body]
/export/gnu/import/git/gitlab/x86-gcc-test/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/../char/string_view.cc:39:
warning: 'static_assert' with non-string message only available with
'-std=c++2c' or '-std=gnu++2c' [-Wc++26-extensions]
/export/gnu/import/git/gitlab/x86-gcc-test/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/../char/string_view.cc:39:
error: expected primary-expression before '{' token [-Wtemplate-body]
/export/gnu/import/git/gitlab/x86-gcc-test/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/../char/string_view.cc:39:
error: expected ')' before '{' token [-Wtemplate-body]
/export/gnu/import/git/gitlab/x86-gcc-test/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/../char/string_view.cc:41:
error: 'requires' only available with '-std=c++20' or '-fconcepts'
[-Wtemplate-body]
/export/gnu/import/git/gitlab/x86-gcc-test/libstdc++-v3/testsuite/27_io/basic_istringstream/cons/wchar_t/../char/string_view.cc:41:
error: expected ',' before '{' token [-Wtemplate-body]
>
> > -- >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
> >
>
--
H.J.
