Hi Patrick, On Tue, Dec 2, 2025 at 3:27 AM Patrick Palka <[email protected]> wrote: > > On Sat, 22 Nov 2025, Yuao Ma wrote: > > > On Sat, Nov 22, 2025 at 12:33 AM Tomasz Kaminski <[email protected]> > > wrote: > > > > > > > > > > > > On Fri, Nov 21, 2025 at 5:11 PM Yuao Ma <[email protected]> wrote: > > >> > > >> On Fri, Nov 21, 2025 at 6:32 PM Tomasz Kaminski <[email protected]> > > >> wrote: > > >> > > > >> > There was a paper submitted before Kona: p3862r0 Postpone > > >> > basic_string::subview and wait for cstring_view [1], > > >> > that according to github papers status [2] have also NB comment. I was > > >> > not able to locale the comment thou. > > >> > So maybe it would be good to have this as patch series for string_view > > >> > (that would contain feature test macro) and then string, > > >> > so we can revert later? > > >> > > > >> > > > >> > [1] > > >> > https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3862r0.html# > > >> > [2] https://github.com/cplusplus/papers/issues/2466 > > >> > > > >> > > >> Thanks for the info! Could you elaborate more on how making this a > > >> patch series helps with reverting? My understanding of P3862R0 is that > > >> it proposed two wording options: one to entirely remove the subview > > >> for string and string_view, and the other to remove the default > > >> parameter argument. > > > > > > Both wording options are changing only basic_string::subview, > > > and not touching subview on string_view at all. > > > > Oh yeah, my mistake. Split into two patches as below. > > > From 668363e4dbf6db6d7cd40899a480256936dcd0ae Mon Sep 17 00:00:00 2001 > > From: Yuao Ma <[email protected]> > > Date: Sat, 22 Nov 2025 00:37:48 +0800 > > Subject: [PATCH 1/2] libstdc++: implement P3044R2 - sub-string_view from > > string (string_view part) > > > > libstdc++-v3/ChangeLog: > > > > * include/bits/version.def: Add string_subview FTM. > > * include/bits/version.h: Regenerate. > > * include/std/string_view: Add subview. > > * testsuite/21_strings/basic_string_view/operations/subview/char.cc: > > New test. > > * > > testsuite/21_strings/basic_string_view/operations/subview/wchar_t.cc: New > > test. > > --- > > libstdc++-v3/include/bits/version.def | 9 ++++ > > libstdc++-v3/include/bits/version.h | 10 ++++ > > libstdc++-v3/include/std/string_view | 10 +++- > > .../operations/subview/char.cc | 52 +++++++++++++++++++ > > .../operations/subview/wchar_t.cc | 52 +++++++++++++++++++ > > 5 files changed, 132 insertions(+), 1 deletion(-) > > create mode 100644 > > libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/char.cc > > create mode 100644 > > libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/wchar_t.cc > > > > diff --git a/libstdc++-v3/include/bits/version.def > > b/libstdc++-v3/include/bits/version.def > > index 29ecf15c7e3..b5575d2399f 100644 > > --- a/libstdc++-v3/include/bits/version.def > > +++ b/libstdc++-v3/include/bits/version.def > > @@ -1934,6 +1934,15 @@ ftms = { > > }; > > }; > > > > +ftms = { > > + name = string_subview; > > + values = { > > + v = 202506; > > + cxxmin = 26; > > + hosted = yes; > > I think we need to add cxx11abi = yes if we don't support this with the > COW string. Wouldn't adding COW string support amount to a few extra > lines in cow_string.h though? >
Yes I added cxx11abi = yes in the latest version of the patch: https://gcc.gnu.org/pipermail/libstdc++/2025-November/064522.html > > + }; > > +}; > > + > > ftms = { > > name = to_underlying; > > values = { > > diff --git a/libstdc++-v3/include/bits/version.h > > b/libstdc++-v3/include/bits/version.h > > index 5901d27113d..413da56b088 100644 > > --- a/libstdc++-v3/include/bits/version.h > > +++ b/libstdc++-v3/include/bits/version.h > > @@ -2161,6 +2161,16 @@ > > #endif /* !defined(__cpp_lib_string_resize_and_overwrite) */ > > #undef __glibcxx_want_string_resize_and_overwrite > > > > +#if !defined(__cpp_lib_string_subview) > > +# if (__cplusplus > 202302L) && _GLIBCXX_HOSTED > > +# define __glibcxx_string_subview 202506L > > +# if defined(__glibcxx_want_all) || defined(__glibcxx_want_string_subview) > > +# define __cpp_lib_string_subview 202506L > > +# endif > > +# endif > > +#endif /* !defined(__cpp_lib_string_subview) */ > > +#undef __glibcxx_want_string_subview > > + > > #if !defined(__cpp_lib_to_underlying) > > # if (__cplusplus >= 202100L) > > # define __glibcxx_to_underlying 202102L > > diff --git a/libstdc++-v3/include/std/string_view > > b/libstdc++-v3/include/std/string_view > > index 842f6ad89af..b226544fa6f 100644 > > --- a/libstdc++-v3/include/std/string_view > > +++ b/libstdc++-v3/include/std/string_view > > @@ -40,9 +40,10 @@ > > #define __glibcxx_want_constexpr_char_traits > > #define __glibcxx_want_constexpr_string_view > > #define __glibcxx_want_freestanding_string_view > > -#define __glibcxx_want_string_view > > #define __glibcxx_want_starts_ends_with > > #define __glibcxx_want_string_contains > > +#define __glibcxx_want_string_subview > > +#define __glibcxx_want_string_view > > #include <bits/version.h> > > > > #if __cplusplus >= 201703L > > @@ -342,6 +343,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > > return basic_string_view{_M_str + __pos, __rlen}; > > } > > > > +#ifdef __glibcxx_string_subview // >= C++26 > > + [[nodiscard]] > > + constexpr basic_string_view > > + subview(size_type __pos = 0, size_type __n = npos) const > > + { return substr(__pos, __n); } > > +#endif > > IIUC since subview is specified as freestanding-deleted, we need to > define it as deleted if we don't support it in freestanding mode. > So perhaps why don't we just always define it in C++26 mode regardless > of whether the FTM is defined? Maybe I'm not understanding the > intent of freestanding-deleted though. > IMHO __glibcxx_string_subview is guarded under HOSTED. Should I explicitly mark this as deleted in freestanding mode? > > + > > [[nodiscard]] > > constexpr int > > compare(basic_string_view __str) const noexcept > > diff --git > > a/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/char.cc > > > > b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/char.cc > > new file mode 100644 > > index 00000000000..296d85af69b > > --- /dev/null > > +++ > > b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/char.cc > > @@ -0,0 +1,52 @@ > > +// { dg-do run { target c++26 } } > > +// { dg-require-effective-target cxx11_abi } > > + > > +#include <string_view> > > +#include <testsuite_hooks.h> > > + > > +#if __STDC_HOSTED__ > > +#include <stdexcept> > > +#endif > > + > > +void test01() { > > + typedef std::string_view::size_type csize_type; > > + typedef std::string_view::const_reference cref; > > + typedef std::string_view::reference ref; > > + csize_type csz01; > > + > > + const char str_lit01[] = "rockaway, pacifica"; > > + const std::string_view str01(str_lit01); > > + std::string_view str02; > > + > > + csz01 = str01.size(); > > + str02 = str01.subview(0, 1); > > + VERIFY(str02 == "r"); > > + str02 = str01.subview(10); > > + VERIFY(str02 == "pacifica"); > > + > > +#if __STDC_HOSTED__ > > + try { > > + str02 = str01.subview(csz01 + 1); > > + VERIFY(false); > > + } catch (std::out_of_range &fail) { > > + VERIFY(true); > > + } catch (...) { > > + VERIFY(false); > > + } > > + > > + try { > > + str02 = str01.subview(csz01); > > + VERIFY(str02.size() == 0); > > + VERIFY(str02.begin() == str01.end()); > > + VERIFY(true); > > + } catch (...) { > > + VERIFY(false); > > + } > > +#endif // HOSTED > > +} > > + > > +int main() { > > + test01(); > > + > > + return 0; > > +} > > diff --git > > a/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/wchar_t.cc > > > > b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/wchar_t.cc > > new file mode 100644 > > index 00000000000..461d1005c65 > > --- /dev/null > > +++ > > b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/subview/wchar_t.cc > > @@ -0,0 +1,52 @@ > > +// { dg-do run { target c++26 } } > > +// { dg-require-effective-target cxx11_abi } > > + > > +#include <string_view> > > +#include <testsuite_hooks.h> > > + > > +#if __STDC_HOSTED__ > > +#include <stdexcept> > > +#endif > > + > > +void test01() { > > + typedef std::wstring_view::size_type csize_type; > > + typedef std::wstring_view::const_reference cref; > > + typedef std::wstring_view::reference ref; > > + csize_type csz01; > > + > > + const wchar_t str_lit01[] = L"rockaway, pacifica"; > > + const std::wstring_view str01(str_lit01); > > + std::wstring_view str02; > > + > > + csz01 = str01.size(); > > + str02 = str01.subview(0, 1); > > + VERIFY(str02 == L"r"); > > + str02 = str01.subview(10); > > + VERIFY(str02 == L"pacifica"); > > + > > +#if __STDC_HOSTED__ > > + try { > > + str02 = str01.subview(csz01 + 1); > > + VERIFY(false); > > + } catch (std::out_of_range &fail) { > > + VERIFY(true); > > + } catch (...) { > > + VERIFY(false); > > + } > > + > > + try { > > + str02 = str01.subview(csz01); > > + VERIFY(str02.size() == 0); > > + VERIFY(str02.begin() == str01.end()); > > + VERIFY(true); > > + } catch (...) { > > + VERIFY(false); > > + } > > +#endif // HOSTED > > +} > > + > > +int main() { > > + test01(); > > + > > + return 0; > > +} > > -- > > 2.51.1 > > * * * Hi Jonathan, Could you please take a look at the updated patch at https://gcc.gnu.org/pipermail/libstdc++/2025-November/064522.html? Thanks, Yuao
