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WIP [libc++][string] P3044R2: sub-string_view from string #147095

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WIP [libc++][string] P3044R2: sub-string_view from string #147095

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554a97e
WIP [libc++][string] P3044R2: sub-`string_view` from `string`
H-G-Hristov Jul 4, 2025
e477951
Renamed test
H-G-Hristov Jul 4, 2025
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9 changes: 9 additions & 0 deletions libcxx/include/string
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Original file line number Diff line number Diff line change
Expand Up @@ -280,6 +280,8 @@ public:
basic_string substr(size_type pos = 0, size_type n = npos) const; // constexpr in C++20, removed in C++23
basic_string substr(size_type pos = 0, size_type n = npos) const&; // since C++23
constexpr basic_string substr(size_type pos = 0, size_type n = npos) &&; // since C++23
constexpr basic_string_view<charT, traits> subview(size_type pos = 0,
size_type n = npos) const; // since C++26
void swap(basic_string& str)
noexcept(allocator_traits<allocator_type>::propagate_on_container_swap::value ||
allocator_traits<allocator_type>::is_always_equal::value); // C++17, constexpr since C++20
Expand Down Expand Up @@ -1745,6 +1747,13 @@ public:
}
# endif

# if _LIBCPP_STD_VER >= 26
_LIBCPP_HIDE_FROM_ABI constexpr basic_string_view<_CharT, _Traits>
subview(size_type __pos = 0, size_type __n = npos) const {
return basic_string_view<_CharT, _Traits>(*this).subview(__pos, __n);
}
# endif

_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void swap(basic_string& __str)
# if _LIBCPP_STD_VER >= 14
_NOEXCEPT;
Expand Down
8 changes: 8 additions & 0 deletions libcxx/include/string_view
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Expand Up @@ -130,6 +130,8 @@ namespace std {
size_type copy(charT* s, size_type n, size_type pos = 0) const; // constexpr in C++20

constexpr basic_string_view substr(size_type pos = 0, size_type n = npos) const;
constexpr basic_string_view subview(size_type pos = 0,
size_type n = npos) const; // freestanding-deleted, since C++26
constexpr int compare(basic_string_view s) const noexcept;
constexpr int compare(size_type pos1, size_type n1, basic_string_view s) const;
constexpr int compare(size_type pos1, size_type n1,
Expand Down Expand Up @@ -465,6 +467,12 @@ public:
: basic_string_view(__assume_valid(), data() + __pos, std::min(__n, size() - __pos));
}

# if _LIBCPP_STD_VER >= 26
_LIBCPP_HIDE_FROM_ABI constexpr basic_string_view subview(size_type __pos = 0, size_type __n = npos) const {
return this->substr(__pos, __n);
}
# endif

_LIBCPP_CONSTEXPR_SINCE_CXX14 int compare(basic_string_view __sv) const _NOEXCEPT {
size_type __rlen = std::min(size(), __sv.size());
int __retval = _Traits::compare(data(), __sv.data(), __rlen);
Expand Down
33 changes: 33 additions & 0 deletions libcxx/test/std/strings/basic.string/string.ops/string_substr/subview.pass.cpp
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@@ -0,0 +1,33 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// REQUIRES: std-at-least-c++26

// <string>

// constexpr basic_string_view<_CharT, _Traits> subview(size_type __pos = 0, size_type __n = npos) const;

#include <cassert>
#include <string>

constexpr bool test() {
std::string s{"Hello cruel world!"};
auto sub = s.subview(6);
assert(sub == "cruel world!");
auto subsub = sub.subview(0, 5);
assert(subsub == "cruel");

return true;
}

int main(int, char**) {
test();
static_assert(test());

return 0;
}
152 changes: 92 additions & 60 deletions libcxx/test/std/strings/string.view/string.view.ops/substr.pass.cpp
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Expand Up @@ -11,6 +11,10 @@
// <string_view>

// constexpr basic_string_view substr(size_type pos = 0, size_type n = npos) const;
// constexpr basic_string_view subview(size_type pos = 0,
// size_type n = npos) const; // freestanding-deleted

// subview is alternative name of substr

// Throws: out_of_range if pos > size().
// Effects: Determines the effective length rlen of the string to reference as the smaller of n and size() - pos.
Expand All @@ -25,15 +29,21 @@
#include "test_macros.h"

template <typename CharT>
void test1(std::basic_string_view<CharT> sv, std::size_t n, size_t pos) {
struct Test {
typedef std::basic_string_view<CharT> (std::basic_string_view<CharT>::*Sub)(
typename std::basic_string_view<CharT>::size_type, typename std::basic_string_view<CharT>::size_type) const;
};

template <typename CharT, typename Test<CharT>::Sub TestSub>
void testDetail(std::basic_string_view<CharT> sv, std::size_t n, size_t pos) {
std::basic_string_view<CharT> sv1;
#ifdef TEST_HAS_NO_EXCEPTIONS
if (pos > sv.size())
return; // would throw if exceptions were enabled
sv1 = sv.substr(pos, n);
sv1 = (sv.*TestSub)(pos, n);
#else
try {
sv1 = sv.substr(pos, n);
sv1 = (sv.*TestSub)(pos, n);
assert(pos <= sv.size());
} catch (const std::out_of_range&) {
assert(pos > sv.size());
Expand All @@ -46,79 +56,101 @@ void test1(std::basic_string_view<CharT> sv, std::size_t n, size_t pos) {
assert(sv[pos + i] == sv1[i]);
}

template <typename CharT>
void test(const CharT* s) {
typedef std::basic_string_view<CharT> string_view_t;
template <typename CharT, typename Test<CharT>::Sub TestSub>
void testCases(const CharT* s) {
std::basic_string_view<CharT> sv(s);

string_view_t sv1(s);
testDetail<CharT, TestSub>(sv, 0, 0);
testDetail<CharT, TestSub>(sv, 1, 0);
testDetail<CharT, TestSub>(sv, 20, 0);
testDetail<CharT, TestSub>(sv, sv.size(), 0);

test1(sv1, 0, 0);
test1(sv1, 1, 0);
test1(sv1, 20, 0);
test1(sv1, sv1.size(), 0);
testDetail<CharT, TestSub>(sv, 100, 3);

test1(sv1, 0, 3);
test1(sv1, 2, 3);
test1(sv1, 100, 3);
testDetail<CharT, TestSub>(sv, 0, std::basic_string_view<CharT>::npos);
testDetail<CharT, TestSub>(sv, 2, std::basic_string_view<CharT>::npos);
testDetail<CharT, TestSub>(sv, sv.size(), std::basic_string_view<CharT>::npos);

test1(sv1, 0, string_view_t::npos);
test1(sv1, 2, string_view_t::npos);
test1(sv1, sv1.size(), string_view_t::npos);
testDetail<CharT, TestSub>(sv, sv.size() + 1, 0);
testDetail<CharT, TestSub>(sv, sv.size() + 1, 1);
testDetail<CharT, TestSub>(sv, sv.size() + 1, std::basic_string_view<CharT>::npos);
}

test1(sv1, sv1.size() + 1, 0);
test1(sv1, sv1.size() + 1, 1);
test1(sv1, sv1.size() + 1, string_view_t::npos);
template <typename CharT>
void testSubs(const CharT* s) {
testCases<CharT, &std::basic_string_view<CharT>::substr>(s);
#if TEST_STD_VER >= 26
testCases<CharT, &std::basic_string_view<CharT>::subview>(s);
#endif // TEST_STD_VER >= 26
}

int main(int, char**) {
test("ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
test("ABCDE");
test("a");
test("");
void test() {
testSubs("ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
testSubs("ABCDE");
testSubs("a");
testSubs("");

#ifndef TEST_HAS_NO_WIDE_CHARACTERS
test(L"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
test(L"ABCDE");
test(L"a");
test(L"");
testSubs(
L"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
testSubs(L"ABCDE");
testSubs(L"a");
testSubs(L"");
#endif

#if TEST_STD_VER >= 11
test(u"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
test(u"ABCDE");
test(u"a");
test(u"");

test(U"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
test(U"ABCDE");
test(U"a");
test(U"");
testSubs(
u"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
testSubs(u"ABCDE");
testSubs(u"a");
testSubs(u"");

testSubs(
U"ABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDEABCDE");
testSubs(U"ABCDE");
testSubs(U"a");
testSubs(U"");
#endif
}

#if TEST_STD_VER >= 14
template <typename Test<char>::Sub TestSub>
constexpr void testConstexprDetail() {
constexpr std::string_view sv{"ABCDE", 5};
{
constexpr std::string_view sv2 = (sv.*TestSub)(0, 3);

static_assert(sv2.size() == 3, "");
static_assert(sv2[0] == 'A', "");
static_assert(sv2[1] == 'B', "");
static_assert(sv2[2] == 'C', "");
}

#if TEST_STD_VER > 11
{
constexpr std::string_view sv1{"ABCDE", 5};

{
constexpr std::string_view sv2 = sv1.substr(0, 3);
static_assert(sv2.size() == 3, "");
static_assert(sv2[0] == 'A', "");
static_assert(sv2[1] == 'B', "");
static_assert(sv2[2] == 'C', "");
}

{
constexpr std::string_view sv2 = sv1.substr(3, 0);
static_assert(sv2.size() == 0, "");
}

{
constexpr std::string_view sv2 = sv1.substr(3, 3);
static_assert(sv2.size() == 2, "");
static_assert(sv2[0] == 'D', "");
static_assert(sv2[1] == 'E', "");
}
constexpr std::string_view sv2 = (sv.*TestSub)(3, 0);
static_assert(sv2.size() == 0, "");
}

{
constexpr std::string_view sv2 = (sv.*TestSub)(3, 3);
static_assert(sv2.size() == 2, "");
static_assert(sv2[0] == 'D', "");
static_assert(sv2[1] == 'E', "");
}
}

void test_constexpr() {
testConstexprDetail<&std::string_view::substr>();
# if TEST_STD_VER >= 26
testConstexprDetail<&std::string_view::subview>();
# endif
}
#endif

int main(int, char**) {
test();
#if TEST_STD_VER >= 14
test_constexpr();
#endif

return 0;
Expand Down
20 changes: 20 additions & 0 deletions libcxx/test/std/strings/string.view/string.view.ops/subview.pass.cpp
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@@ -0,0 +1,20 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// REQUIRES: std-at-least-c++26

// <string_view>

// constexpr basic_string_view subview(size_type pos = 0,
// size_type n = npos) const; // freestanding-deleted

int main(int, char**) {
// This test is intentionally empty because subview is an alias for substr
// and is tested in substr.pass.cpp.
Comment on lines +17 to +18
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Looks like we don't need this file.

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I am not sure what the current practice about function aliases is. Normally we want a test file per function. This one is to tell the user what to look at. Are there any similar cases in the library?

return 0;
}
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