├── .github └── workflows │ └── ci.yml ├── CMakeLists.txt ├── LICENSE ├── README.md ├── include └── bev │ └── string_view.hpp └── test ├── CMakeLists.txt └── tests.cpp /.github/workflows/ci.yml: -------------------------------------------------------------------------------- 1 | name: Continuous Integration 2 | 3 | on: 4 | push: 5 | branches: 6 | - master 7 | 8 | pull_request: 9 | branches: 10 | - master 11 | 12 | jobs: 13 | tests: 14 | runs-on: ubuntu-latest 15 | 16 | steps: 17 | - uses: actions/checkout@v1 18 | 19 | - uses: friendlyanon/fetch-core-count@v1 20 | id: cores 21 | 22 | - name: Configure 23 | run: cmake -S test -B build -D CMAKE_BUILD_TYPE=Release 24 | 25 | - name: Build 26 | run: cmake --build build --config Release 27 | -j ${{ steps.cores.outputs.plus_one }} 28 | 29 | - name: Run 30 | working-directory: build 31 | run: ctest -C Release -j ${{ steps.cores.outputs.count }} 32 | -------------------------------------------------------------------------------- /CMakeLists.txt: -------------------------------------------------------------------------------- 1 | cmake_minimum_required(VERSION 3.12) 2 | 3 | project(string_view 4 | VERSION 1.0.0 5 | DESCRIPTION "A string_view implementation that can remember if it was a c-string once" 6 | HOMEPAGE_URL "https://github.com/lava/string_view" 7 | LANGUAGES CXX) 8 | 9 | # ---- Warning guard ---- 10 | 11 | # Protect dependents from this project's warnings if the guard isn't disabled 12 | set(string_view_warning_guard "SYSTEM") 13 | if(string_view_INCLUDE_WITHOUT_SYSTEM) 14 | set(string_view_warning_guard "") 15 | endif() 16 | 17 | # ---- Declare library ---- 18 | 19 | add_library(string_view INTERFACE) 20 | add_library(bev::string_view ALIAS string_view) 21 | 22 | target_include_directories(string_view 23 | ${string_view_warning_guard} 24 | INTERFACE 25 | "$") 26 | 27 | target_compile_features(string_view INTERFACE cxx_std_17) 28 | 29 | # ---- Install ---- 30 | 31 | include(CMakePackageConfigHelpers) 32 | include(GNUInstallDirs) 33 | 34 | set(string_view_directory "string_view-${PROJECT_VERSION}") 35 | set(string_view_include_directory 36 | "${CMAKE_INSTALL_INCLUDEDIR}/${string_view_directory}") 37 | 38 | install(TARGETS string_view 39 | EXPORT string_viewTargets 40 | INCLUDES DESTINATION "${string_view_include_directory}") 41 | 42 | set(string_view_install_cmakedir 43 | "${CMAKE_INSTALL_LIBDIR}/cmake/${string_view_directory}") 44 | 45 | write_basic_package_version_file( 46 | string_viewConfigVersion.cmake 47 | VERSION "${PROJECT_VERSION}" 48 | COMPATIBILITY SameMajorVersion 49 | ARCH_INDEPENDENT) 50 | 51 | install(EXPORT string_viewTargets 52 | FILE string_viewConfig.cmake 53 | NAMESPACE bev:: 54 | DESTINATION "${string_view_install_cmakedir}") 55 | 56 | install(FILES 57 | "${PROJECT_BINARY_DIR}/string_viewConfigVersion.cmake" 58 | DESTINATION "${string_view_install_cmakedir}") 59 | 60 | install(DIRECTORY "${PROJECT_SOURCE_DIR}/include/" 61 | DESTINATION "${string_view_include_directory}") 62 | 63 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | 635 | Copyright (C) 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Copyright (C) 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # A `string_view` that remembers if it was a C string 2 | 3 | # The Problem 4 | 5 | When interfacing with C APIs, one often encounters functions that 6 | take a null-terminated byte array as an argument, e.g. 7 | 8 | 9 | int open(const char *pathname, int flags); 10 | 11 | 12 | From a C++ context, a C call like this is often moved into some convenience 13 | wrapper function that provides additional type safety, for example 14 | 15 | 16 | fd_type open(const std::string& pathname, int flags = 0) { 17 | return ::open(pathname.c_str(), flags); 18 | } 19 | 20 | 21 | One problem with this function is that when it is called with a string 22 | literal as argument 23 | 24 | 25 | auto fd = open("/dev/null"); 26 | 27 | 28 | a temporary `std::string` object will be created that needs to copy the 29 | string literal into an internal buffer. 30 | 31 | In C++17, the new `std::string_view` class was introduced into the standard 32 | to avoid this unnecessary copy. It is a non-owning view that can be 33 | transparently used for `std::string`, `const char*` or any other form of byte 34 | buffer. 35 | 36 | However, in this particular example it only moves the issue to another place: 37 | Since the `string_view` is not necessarily null-terminated, it is not possible 38 | to simply forward the contained `const char*` to the C function. Instead, if the 39 | view is not null-terminated, a copy needs to be created. 40 | 41 | The catch-22 here is that it is *impossible* to safely check whether a given 42 | string_view is null-terminated, since the byte we'd need to check may not even 43 | be mapped to valid memory. So we're required to write code like this: 44 | 45 | 46 | fd_type open(std::string_view sv, int flags = 0) { 47 | return ::open(std::string{sv}.c_str(), flags); 48 | } 49 | 50 | 51 | Of course, this is a well-known problem. To quote the original string_view 52 | proposal from 2013: 53 | 54 | > We could imagine inventing a more complex interface that records whether the 55 | input string was null-terminated, giving the user the option to use that 56 | string when trying to pass a string_view to a legacy or C function expecting 57 | a null-terminated `const char*`. This proposal doesn't include such an 58 | interface because it would make string_view bigger or more expensive, and 59 | because there's no existing practice to guide us toward the right interface. 60 | 61 | # The Solution 62 | 63 | When *receiving* a string_view we can not possibly tell whether it is 64 | null-terminated or not, however when *creating* a string_view the situation is 65 | not so bleak: When a string_view is created from a `std::string` or from a 66 | string literal, it is guaranteed that a null byte exists after the string. 67 | 68 | And when creating substrings or removing suffixes, at least we know that *some* 69 | byte exists after the buffer, so at least we can check if it is null or not 70 | without accessing invalid memory. 71 | 72 | So all we have to do is to remember this information from the construction of 73 | the `string_view`, and then we could implement a `is_cstring()` member function 74 | that can be used to tell us whether we can directly use the pointer as a C 75 | string or not: 76 | 77 | 78 | fd_type open(bev::string_view sv, int flags = 0) { 79 | if (sv.is_cstring()) 80 | return ::open(sv.data(), flags); 81 | else 82 | return ::open(std::string{sv}.c_str(), flags); 83 | } 84 | 85 | 86 | Sadly, just adding a `bool` member to capture this single bit of information 87 | would most likely increase the size of the struct by 8 bytes in total to 88 | preserve alignment, a 50% increase. That's less than ideal. 89 | 90 | One common technique to avoid this is the "bit stuffing" of pointers: When a 91 | pointer has certain alignment requirements, its bottom-most bits must be always 92 | zero and can be repurposed to store flags. However that's not possible here, 93 | since in the most common case the pointer will be a `const char*`, which doesnt 94 | have any alignment requirements. 95 | 96 | There is one other member of `string_view`, namely it's length. Could we 97 | possibly find any unused bits in there? Why, yes, indeed. In libstdc++, this 98 | is implemented as 99 | 100 | 101 | return (npos - sizeof(size_type) - sizeof(void*)) 102 | / sizeof(value_type) / 4; 103 | 104 | 105 | So it already is guaranteed to have at least two unused bits. In `libcxx` this 106 | actually returns `npos`, but we only need a single bit so there should be no 107 | problem to reduce this to `npos / 2`. Very few people work with strings larger 108 | than 8 EiB, after all. We call this the `safederef flag` because, well, naming 109 | is hard. 110 | 111 | After all this exposition the actual code is embarassingly simple: 112 | 113 | 114 | bool string_view::is_cstring() 115 | { 116 | if (test_safederef_flag(len_)) 117 | return str_[this->length()] == 0; 118 | return false; 119 | } 120 | 121 | The [full list of changes][1] is slightly bigger, but it still turned out to be 122 | far less ugly than I had anticipated. 123 | 124 | We could also check once at construction and cache the result, but doing it 125 | on every call also covers changes to the string after the `string_view` was 126 | created. 127 | 128 | So, tl;dr: 129 | 130 | - The highest bit of `len_` is reserved as a `safederef` flag 131 | - When creating a string view from a std::string or from a `const char*`, this 132 | is set to true. 133 | - When copying a string_view or when creating substring, the flag is preserved. 134 | - Then `is_cstring()` can be implemented as `str_[len_] == 0`. 135 | 136 | 137 | [1]: https://github.com/lava/string_view/commit/abcf453359c8d1ba74d5686d0f1cdfec67d67380 138 | 139 | # The Caveat 140 | 141 | So, can we just call it a day and add this to the standard? No. 142 | 143 | Even though the binary layout is the same as `std::string_view` is exactly the 144 | same (if you're adventurous you could even 145 | `reinterpret_cast(&std::string_view)` and everything should 146 | work), the semantics of the `len_` field changed and passing a new string_view 147 | to a function expecting the previous version would produce weird results. 148 | So this would be an ABI break. 149 | 150 | Also, I didn't actually bother to propely benchmark this, so I have no proof 151 | that this would even result in significant performance gains. 152 | 153 | That said, if you *did* benchmark and you see there are unnecessary string 154 | copies going on when calling C functions, feel free to use the string_view class 155 | in this repository as a drop-in replacement. 156 | -------------------------------------------------------------------------------- /include/bev/string_view.hpp: -------------------------------------------------------------------------------- 1 | // An implementation of the `std::string_view` class template, with the addition 2 | // of a new `is_cstring()` member function that can be used to avoid unnecessary 3 | // copies in some situations. 4 | // 5 | // This implementation of `std::string_view` was originally written as part of 6 | // the GNU ISO C++ Library. The original code is available under the GNU GPLv3 7 | // with the GCC Runtime Library Exception at gcc.gnu.org/git/gcc.git 8 | // 9 | // Interface Changes: 10 | // * A new member function `basic_string_view::is_cstring()` that tells 11 | // whether `.data()` returns a null-terminated byte array. 12 | // Note that this function is conservative in the sense that it may return 13 | // `false` even if `.data()` would be null-terminated, for example in the 14 | // presence of embedded null bytes. 15 | // * A new constructor from `std::string` was added, since it is not possible 16 | // to replicate the original string_view interface of adding new user-defined 17 | // conversions to std::string. 18 | // * For the same reasons, the string_view literal operators have been renamed 19 | // to `_sv` and dont live in namespace `std` anymore. 20 | // 21 | // Internal Changes: 22 | // * General reformatting required by moving the class out of the `std` namespace, 23 | // in particular removal of the underscore and double-underscore variable name 24 | // prefixes that are reserved for use by the standard library. 25 | // * Removal of all libstdc++ internal functions. This means that the class can 26 | // be compiled against any standard library. In particular this includes many 27 | // debug assertions and checks. 28 | // * Only supports 64-bit size_t (the main reason being that I only copied the 29 | // 64-bit version of MurmurHash3, and I don't have a 32 bit system for 30 | // testing available) 31 | // * Removed support for char8_t (since my compiler doesnt have it yet) 32 | 33 | #pragma once 34 | 35 | #include 36 | #include 37 | #include 38 | #include 39 | #include 40 | 41 | namespace bev { 42 | 43 | /** 44 | * @brief A non-owning reference to a string. 45 | * 46 | * @tparam CharT Type of character 47 | * @tparam Traits Traits for character type, defaults to 48 | * std::char_traits. 49 | * 50 | * A basic_string_view looks like this: 51 | * 52 | * @code 53 | * CharT* str_ 54 | * size_t len_ 55 | * @endcode 56 | */ 57 | template> 58 | class basic_string_view 59 | { 60 | static_assert(!std::is_array_v); 61 | static_assert(std::is_trivial_v && std::is_standard_layout_v); 62 | static_assert(std::is_same_v); 63 | 64 | // bitmask for accessing the `safederef` flag bit in `len_`. 65 | static const size_t safederef_flag_mask = 1ull << (CHAR_BIT*sizeof(size_t)-1); 66 | static size_t set_safederef_bit(size_t x) { return x | safederef_flag_mask; } 67 | static size_t clear_safederef_bit(size_t x) { return x & ~safederef_flag_mask; } 68 | static bool test_safederef_bit(size_t x) { return x & safederef_flag_mask; } 69 | 70 | public: 71 | 72 | // types 73 | using traits_type = Traits; 74 | using value_type = CharT; 75 | using pointer = value_type*; 76 | using const_pointer = const value_type*; 77 | using reference = value_type&; 78 | using const_reference = const value_type&; 79 | using const_iterator = const value_type*; 80 | using iterator = const_iterator; 81 | using const_reverse_iterator = std::reverse_iterator; 82 | using reverse_iterator = const_reverse_iterator; 83 | using size_type = size_t; 84 | using difference_type = ptrdiff_t; 85 | static constexpr size_type npos = size_type(-1); 86 | 87 | // [string.view.cons], construction and assignment 88 | 89 | constexpr 90 | basic_string_view() noexcept 91 | : len_{0}, str_{nullptr} 92 | { } 93 | 94 | constexpr basic_string_view(const basic_string_view&) noexcept = default; 95 | 96 | constexpr basic_string_view(const CharT* str) noexcept 97 | : len_{set_safederef_bit(traits_type::length(str))} 98 | , str_{str} 99 | { } 100 | 101 | constexpr 102 | basic_string_view(const CharT* str, size_type len) noexcept 103 | : len_{len}, str_{str} 104 | { } 105 | 106 | constexpr basic_string_view& 107 | operator=(const basic_string_view&) noexcept = default; 108 | 109 | // non-standard constructors 110 | basic_string_view(const std::basic_string& s) 111 | : len_{set_safederef_bit(s.size())}, str_{s.data()} 112 | {} 113 | 114 | basic_string_view(std::basic_string&&) = delete; 115 | 116 | private: 117 | struct can_test_safederef {}; 118 | 119 | basic_string_view(const CharT* str, size_type len, can_test_safederef) 120 | : len_(set_safederef_bit(len)), str_(str) 121 | {} 122 | 123 | public: 124 | 125 | // non-standard interface 126 | bool is_cstring() 127 | { 128 | if (test_safederef_bit(len_)) 129 | return str_[this->length()] == CharT{0}; 130 | return false; 131 | } 132 | 133 | // [string.view.iterators], iterator support 134 | 135 | constexpr const_iterator 136 | begin() const noexcept 137 | { return this->str_; } 138 | 139 | constexpr const_iterator 140 | end() const noexcept 141 | { return this->str_ + this->length(); } 142 | 143 | constexpr const_iterator 144 | cbegin() const noexcept 145 | { return this->str_; } 146 | 147 | constexpr const_iterator 148 | cend() const noexcept 149 | { return this->str_ + this->length(); } 150 | 151 | constexpr const_reverse_iterator 152 | rbegin() const noexcept 153 | { return const_reverse_iterator(this->end()); } 154 | 155 | constexpr const_reverse_iterator 156 | rend() const noexcept 157 | { return const_reverse_iterator(this->begin()); } 158 | 159 | constexpr const_reverse_iterator 160 | crbegin() const noexcept 161 | { return const_reverse_iterator(this->end()); } 162 | 163 | constexpr const_reverse_iterator 164 | crend() const noexcept 165 | { return const_reverse_iterator(this->begin()); } 166 | 167 | // [string.view.capacity], capacity 168 | 169 | constexpr size_type 170 | size() const noexcept 171 | { return this->length(); } 172 | 173 | constexpr size_type 174 | length() const noexcept 175 | { return clear_safederef_bit(len_); } 176 | 177 | constexpr size_type 178 | max_size() const noexcept 179 | { 180 | return (npos - sizeof(size_type) - sizeof(void*)) 181 | / sizeof(value_type) / 4; 182 | } 183 | 184 | [[nodiscard]] constexpr bool 185 | empty() const noexcept 186 | { return length() == 0; } 187 | 188 | // [string.view.access], element access 189 | 190 | constexpr const_reference 191 | operator[](size_type pos) const noexcept 192 | { 193 | return *(this->str_ + pos); 194 | } 195 | 196 | constexpr const_reference 197 | at(size_type pos) const 198 | { 199 | if (pos >= this->length()) 200 | throw std::out_of_range("basic_string_view::at"); 201 | return *(this->str_ + pos); 202 | } 203 | 204 | constexpr const_reference 205 | front() const noexcept 206 | { 207 | return *this->str_; 208 | } 209 | 210 | constexpr const_reference 211 | back() const noexcept 212 | { 213 | return *(this->str_ + this->length() - 1); 214 | } 215 | 216 | constexpr const_pointer 217 | data() const noexcept 218 | { return this->str_; } 219 | 220 | // [string.view.modifiers], modifiers: 221 | 222 | constexpr void 223 | remove_prefix(size_type n) noexcept 224 | { 225 | this->str_ += n; 226 | this->length() -= n; 227 | } 228 | 229 | constexpr void 230 | remove_suffix(size_type n) noexcept 231 | { this->length() -= n; } 232 | 233 | constexpr void 234 | swap(basic_string_view& sv) noexcept 235 | { 236 | auto tmp = *this; 237 | *this = sv; 238 | sv = tmp; 239 | } 240 | 241 | // [string.view.ops], string operations: 242 | 243 | size_type 244 | copy(CharT* str, size_type n, size_type pos = 0) const 245 | { 246 | const size_type rlen = std::min(n, this->length() - pos); 247 | // _GLIBCXX_RESOLVE_LIB_DEFECTS 248 | // 2777. basic_string_view::copy should use char_traits::copy 249 | traits_type::copy(str, data() + pos, rlen); 250 | return rlen; 251 | } 252 | 253 | constexpr basic_string_view 254 | substr(size_type pos = 0, size_type n = npos) const noexcept(false) 255 | { 256 | const size_type rlen = std::min(n, this->length() - pos); 257 | if (test_safederef_bit(len_)) 258 | return basic_string_view{str_ + pos, rlen, can_test_safederef{}}; 259 | return basic_string_view{str_ + pos, rlen}; 260 | } 261 | 262 | constexpr int 263 | compare(basic_string_view str) const noexcept 264 | { 265 | const size_type rlen = std::min(length(), str.length()); 266 | int ret = traits_type::compare(this->str_, str.str_, rlen); 267 | if (ret == 0) 268 | ret = s_compare(length(), str.length()); 269 | return ret; 270 | } 271 | 272 | constexpr int 273 | compare(size_type pos1, size_type n1, basic_string_view str) const 274 | { return this->substr(pos1, n1).compare(str); } 275 | 276 | constexpr int 277 | compare(size_type pos1, size_type n1, 278 | basic_string_view str, size_type pos2, size_type n2) const 279 | { 280 | return this->substr(pos1, n1).compare(str.substr(pos2, n2)); 281 | } 282 | 283 | constexpr int 284 | compare(const CharT* str) const noexcept 285 | { return this->compare(basic_string_view{str}); } 286 | 287 | constexpr int 288 | compare(size_type pos1, size_type n1, const CharT* str) const 289 | { return this->substr(pos1, n1).compare(basic_string_view{str}); } 290 | 291 | constexpr int 292 | compare(size_type pos1, size_type n1, 293 | const CharT* str, size_type n2) const noexcept(false) 294 | { 295 | return this->substr(pos1, n1) 296 | .compare(basic_string_view(str, n2)); 297 | } 298 | 299 | constexpr bool 300 | starts_with(basic_string_view x) const noexcept 301 | { return this->substr(0, x.size()) == x; } 302 | 303 | constexpr bool 304 | starts_with(CharT x) const noexcept 305 | { return !this->empty() && traits_type::eq(this->front(), x); } 306 | 307 | constexpr bool 308 | starts_with(const CharT* x) const noexcept 309 | { return this->starts_with(basic_string_view(x)); } 310 | 311 | constexpr bool 312 | ends_with(basic_string_view x) const noexcept 313 | { 314 | return this->size() >= x.size() 315 | && this->compare(this->size() - x.size(), npos, x) == 0; 316 | } 317 | 318 | constexpr bool 319 | ends_with(CharT x) const noexcept 320 | { return !this->empty() && traits_type::eq(this->back(), x); } 321 | 322 | constexpr bool 323 | ends_with(const CharT* x) const noexcept 324 | { return this->ends_with(basic_string_view(x)); } 325 | 326 | // [string.view.find], searching 327 | 328 | constexpr size_type 329 | find(basic_string_view str, size_type pos = 0) const noexcept 330 | { return this->find(str.str_, pos, str.length()); } 331 | 332 | constexpr size_type 333 | find(CharT c, size_type pos = 0) const noexcept; 334 | 335 | constexpr size_type 336 | find(const CharT* str, size_type pos, size_type n) const noexcept; 337 | 338 | constexpr size_type 339 | find(const CharT* str, size_type pos = 0) const noexcept 340 | { return this->find(str, pos, traits_type::length(str)); } 341 | 342 | constexpr size_type 343 | rfind(basic_string_view str, size_type pos = npos) const noexcept 344 | { return this->rfind(str.str_, pos, str.length()); } 345 | 346 | constexpr size_type 347 | rfind(CharT c, size_type pos = npos) const noexcept; 348 | 349 | constexpr size_type 350 | rfind(const CharT* str, size_type pos, size_type n) const noexcept; 351 | 352 | constexpr size_type 353 | rfind(const CharT* str, size_type pos = npos) const noexcept 354 | { return this->rfind(str, pos, traits_type::length(str)); } 355 | 356 | constexpr size_type 357 | find_first_of(basic_string_view str, size_type pos = 0) const noexcept 358 | { return this->find_first_of(str.str_, pos, str.length()); } 359 | 360 | constexpr size_type 361 | find_first_of(CharT c, size_type pos = 0) const noexcept 362 | { return this->find(c, pos); } 363 | 364 | constexpr size_type 365 | find_first_of(const CharT* str, size_type pos, 366 | size_type n) const noexcept; 367 | 368 | constexpr size_type 369 | find_first_of(const CharT* str, size_type pos = 0) const noexcept 370 | { return this->find_first_of(str, pos, traits_type::length(str)); } 371 | 372 | constexpr size_type 373 | find_last_of(basic_string_view str, 374 | size_type pos = npos) const noexcept 375 | { return this->find_last_of(str.str_, pos, str.length()); } 376 | 377 | constexpr size_type 378 | find_last_of(CharT c, size_type pos=npos) const noexcept 379 | { return this->rfind(c, pos); } 380 | 381 | constexpr size_type 382 | find_last_of(const CharT* str, size_type pos, 383 | size_type n) const noexcept; 384 | 385 | constexpr size_type 386 | find_last_of(const CharT* str, size_type pos = npos) const noexcept 387 | { return this->find_last_of(str, pos, traits_type::length(str)); } 388 | 389 | constexpr size_type 390 | find_first_not_of(basic_string_view str, 391 | size_type pos = 0) const noexcept 392 | { return this->find_first_not_of(str.str_, pos, str.length()); } 393 | 394 | constexpr size_type 395 | find_first_not_of(CharT c, size_type pos = 0) const noexcept; 396 | 397 | constexpr size_type 398 | find_first_not_of(const CharT* str, 399 | size_type pos, size_type n) const noexcept; 400 | 401 | constexpr size_type 402 | find_first_not_of(const CharT* str, size_type pos = 0) const noexcept 403 | { 404 | return this->find_first_not_of(str, pos, 405 | traits_type::length(str)); 406 | } 407 | 408 | constexpr size_type 409 | find_last_not_of(basic_string_view str, 410 | size_type pos = npos) const noexcept 411 | { return this->find_last_not_of(str.str_, pos, str.length()); } 412 | 413 | constexpr size_type 414 | find_last_not_of(CharT c, size_type pos = npos) const noexcept; 415 | 416 | constexpr size_type 417 | find_last_not_of(const CharT* str, 418 | size_type pos, size_type n) const noexcept; 419 | 420 | constexpr size_type 421 | find_last_not_of(const CharT* str, 422 | size_type pos = npos) const noexcept 423 | { 424 | return this->find_last_not_of(str, pos, 425 | traits_type::length(str)); 426 | } 427 | 428 | private: 429 | 430 | // Return the difference between n1 and n2, clamped to the range of int. 431 | static constexpr int 432 | s_compare(size_type n1, size_type n2) noexcept 433 | { 434 | const difference_type diff = n1 - n2; 435 | if (diff > INT_MAX) 436 | return INT_MAX; 437 | if (diff < INT_MIN) 438 | return INT_MIN; 439 | return static_cast(diff); 440 | } 441 | 442 | size_t len_; 443 | const CharT* str_; 444 | }; 445 | 446 | // [string.view.comparison], non-member basic_string_view comparison function 447 | 448 | namespace detail { 449 | // Identity transform to create a non-deduced context, so that only one 450 | // argument participates in template argument deduction and the other 451 | // argument gets implicitly converted to the deduced type. See n3766.html. 452 | template 453 | using identity = std::common_type_t; 454 | } // namespace detail 455 | 456 | template 457 | constexpr bool 458 | operator==(basic_string_view x, 459 | basic_string_view y) noexcept 460 | { return x.size() == y.size() && x.compare(y) == 0; } 461 | 462 | template 463 | constexpr bool 464 | operator==(basic_string_view x, 465 | detail::identity> y) noexcept 466 | { return x.size() == y.size() && x.compare(y) == 0; } 467 | 468 | template 469 | constexpr bool 470 | operator==(detail::identity> x, 471 | basic_string_view y) noexcept 472 | { return x.size() == y.size() && x.compare(y) == 0; } 473 | 474 | template 475 | constexpr bool 476 | operator!=(basic_string_view x, 477 | basic_string_view y) noexcept 478 | { return !(x == y); } 479 | 480 | template 481 | constexpr bool 482 | operator!=(basic_string_view x, 483 | detail::identity> y) noexcept 484 | { return !(x == y); } 485 | 486 | template 487 | constexpr bool 488 | operator!=(detail::identity> x, 489 | basic_string_view y) noexcept 490 | { return !(x == y); } 491 | 492 | template 493 | constexpr bool 494 | operator< (basic_string_view x, 495 | basic_string_view y) noexcept 496 | { return x.compare(y) < 0; } 497 | 498 | template 499 | constexpr bool 500 | operator< (basic_string_view x, 501 | detail::identity> y) noexcept 502 | { return x.compare(y) < 0; } 503 | 504 | template 505 | constexpr bool 506 | operator< (detail::identity> x, 507 | basic_string_view y) noexcept 508 | { return x.compare(y) < 0; } 509 | 510 | template 511 | constexpr bool 512 | operator> (basic_string_view x, 513 | basic_string_view y) noexcept 514 | { return x.compare(y) > 0; } 515 | 516 | template 517 | constexpr bool 518 | operator> (basic_string_view x, 519 | detail::identity> y) noexcept 520 | { return x.compare(y) > 0; } 521 | 522 | template 523 | constexpr bool 524 | operator> (detail::identity> x, 525 | basic_string_view y) noexcept 526 | { return x.compare(y) > 0; } 527 | 528 | template 529 | constexpr bool 530 | operator<=(basic_string_view x, 531 | basic_string_view y) noexcept 532 | { return x.compare(y) <= 0; } 533 | 534 | template 535 | constexpr bool 536 | operator<=(basic_string_view x, 537 | detail::identity> y) noexcept 538 | { return x.compare(y) <= 0; } 539 | 540 | template 541 | constexpr bool 542 | operator<=(detail::identity> x, 543 | basic_string_view y) noexcept 544 | { return x.compare(y) <= 0; } 545 | 546 | template 547 | constexpr bool 548 | operator>=(basic_string_view x, 549 | basic_string_view y) noexcept 550 | { return x.compare(y) >= 0; } 551 | 552 | template 553 | constexpr bool 554 | operator>=(basic_string_view x, 555 | detail::identity> y) noexcept 556 | { return x.compare(y) >= 0; } 557 | 558 | template 559 | constexpr bool 560 | operator>=(detail::identity> x, 561 | basic_string_view y) noexcept 562 | { return x.compare(y) >= 0; } 563 | 564 | // [string.view.io], Inserters and extractors 565 | template 566 | inline std::basic_ostream& 567 | operator<<(std::basic_ostream& os, 568 | basic_string_view str) 569 | { 570 | auto len = str.length(); 571 | for (size_t i=0; i; 579 | using wstring_view = basic_string_view; 580 | using u16string_view = basic_string_view; 581 | using u32string_view = basic_string_view; 582 | 583 | // string view literals 584 | 585 | inline constexpr basic_string_view 586 | operator""_sv(const char* str, size_t len) noexcept 587 | { return basic_string_view{str, len}; } 588 | 589 | inline constexpr basic_string_view 590 | operator""_sv(const wchar_t* str, size_t len) noexcept 591 | { return basic_string_view{str, len}; } 592 | 593 | inline constexpr basic_string_view 594 | operator""_sv(const char16_t* str, size_t len) noexcept 595 | { return basic_string_view{str, len}; } 596 | 597 | inline constexpr basic_string_view 598 | operator""_sv(const char32_t* str, size_t len) noexcept 599 | { return basic_string_view{str, len}; } 600 | 601 | 602 | // Implementation 603 | 604 | template 605 | constexpr typename basic_string_view::size_type 606 | basic_string_view:: 607 | find(const CharT* str, size_type pos, size_type n) const noexcept 608 | { 609 | if (n == 0) 610 | return pos <= length() ? pos : npos; 611 | 612 | if (n <= length()) { 613 | for (; pos <= length() - n; ++pos) 614 | if (traits_type::eq(this->str_[pos], str[0]) 615 | && traits_type::compare(this->str_ + pos + 1, 616 | str + 1, n - 1) == 0) 617 | return pos; 618 | } 619 | return npos; 620 | } 621 | 622 | template 623 | constexpr typename basic_string_view::size_type 624 | basic_string_view::find( 625 | CharT c, size_type pos) const noexcept 626 | { 627 | size_type ret = npos; 628 | if (pos < length()) 629 | { 630 | const size_type n = length() - pos; 631 | const CharT* p = traits_type::find(this->str_ + pos, n, c); 632 | if (p) 633 | ret = p - this->str_; 634 | } 635 | return ret; 636 | } 637 | 638 | template 639 | constexpr typename basic_string_view::size_type 640 | basic_string_view:: 641 | rfind(const CharT* str, size_type pos, size_type n) const noexcept 642 | { 643 | if (n <= length()) { 644 | pos = std::min(size_type(length() - n), pos); 645 | do { 646 | if (traits_type::compare(this->str_ + pos, str, n) == 0) 647 | return pos; 648 | } while (pos-- > 0); 649 | } 650 | return npos; 651 | } 652 | 653 | template 654 | constexpr typename basic_string_view::size_type 655 | basic_string_view:: 656 | rfind(CharT c, size_type pos) const noexcept 657 | { 658 | size_type size = length(); 659 | if (size > 0) { 660 | if (--size > pos) 661 | size = pos; 662 | for (++size; size-- > 0; ) 663 | if (traits_type::eq(this->str_[size], c)) 664 | return size; 665 | } 666 | return npos; 667 | } 668 | 669 | template 670 | constexpr typename basic_string_view::size_type 671 | basic_string_view:: 672 | find_first_of(const CharT* str, size_type pos, 673 | size_type n) const noexcept 674 | { 675 | for (; n && pos < length(); ++pos) { 676 | const CharT* p = traits_type::find(str, n, 677 | this->str_[pos]); 678 | if (p) 679 | return pos; 680 | } 681 | return npos; 682 | } 683 | 684 | template 685 | constexpr typename basic_string_view::size_type 686 | basic_string_view:: 687 | find_last_of(const CharT* str, size_type pos, 688 | size_type n) const noexcept 689 | { 690 | size_type size = this->size(); 691 | if (size && n) 692 | { 693 | if (--size > pos) 694 | size = pos; 695 | do 696 | { 697 | if (traits_type::find(str, n, this->str_[size])) 698 | return size; 699 | } 700 | while (size-- != 0); 701 | } 702 | return npos; 703 | } 704 | 705 | template 706 | constexpr typename basic_string_view::size_type 707 | basic_string_view::find_first_not_of( 708 | const CharT* str, size_type pos, size_type n) const noexcept 709 | { 710 | for (; pos < length(); ++pos) 711 | if (!traits_type::find(str, n, this->str_[pos])) 712 | return pos; 713 | return npos; 714 | } 715 | 716 | template 717 | constexpr typename basic_string_view::size_type 718 | basic_string_view::find_first_not_of( 719 | CharT c, size_type pos) const noexcept 720 | { 721 | for (; pos < length(); ++pos) 722 | if (!traits_type::eq(this->str_[pos], c)) 723 | return pos; 724 | return npos; 725 | } 726 | 727 | template 728 | constexpr typename basic_string_view::size_type 729 | basic_string_view::find_last_not_of( 730 | const CharT* str, 731 | size_type pos, 732 | size_type n) const noexcept 733 | { 734 | size_type size = length(); 735 | if (size) { 736 | if (--size > pos) 737 | size = pos; 738 | do { 739 | if (!traits_type::find(str, n, this->str_[size])) 740 | return size; 741 | } 742 | while (size--); 743 | } 744 | return npos; 745 | } 746 | 747 | template 748 | constexpr typename basic_string_view::size_type 749 | basic_string_view::find_last_not_of(CharT c, size_type pos) const noexcept 750 | { 751 | size_type size = length(); 752 | if (size) { 753 | if (--size > pos) 754 | size = pos; 755 | do { 756 | if (!traits_type::eq(this->str_[size], c)) 757 | return size; 758 | } while (size--); 759 | } 760 | return npos; 761 | } 762 | 763 | // namespace for the implementation of the string_view hash 764 | namespace detail { 765 | 766 | inline std::size_t unaligned_load_(const char* p) 767 | { 768 | std::size_t result; 769 | __builtin_memcpy(&result, p, sizeof(result)); 770 | return result; 771 | } 772 | 773 | // Loads n bytes, where 1 <= n < 8. 774 | inline std::size_t load_bytes_(const char* p, int n) 775 | { 776 | std::size_t result = 0; 777 | --n; 778 | do 779 | result = (result << 8) + static_cast(p[n]); 780 | while (--n >= 0); 781 | return result; 782 | } 783 | 784 | inline std::size_t shift_mix_(std::size_t v) 785 | { return v ^ (v >> 47);} 786 | 787 | // Implementation of Murmur hash for 64-bit size_t. 788 | size_t hash_bytes_(const void* ptr, size_t len, size_t seed) 789 | { 790 | constexpr const size_t mul = (((size_t) 0xc6a4a793UL) << 32UL) 791 | + (size_t) 0x5bd1e995UL; 792 | const char* const buf = static_cast(ptr); 793 | 794 | // Remove the bytes not divisible by the sizeof(size_t). This 795 | // allows the main loop to process the data as 64-bit integers. 796 | const size_t len_aligned = len & ~(size_t)0x7; 797 | const char* const end = buf + len_aligned; 798 | size_t hash = seed ^ (len * mul); 799 | for (const char* p = buf; p != end; p += 8) { 800 | const size_t data = shift_mix_(unaligned_load_(p) * mul) * mul; 801 | hash ^= data; 802 | hash *= mul; 803 | } 804 | if ((len & 0x7) != 0) { 805 | const size_t data = load_bytes_(end, len & 0x7); 806 | hash ^= data; 807 | hash *= mul; 808 | } 809 | hash = shift_mix_(hash) * mul; 810 | hash = shift_mix_(hash); 811 | return hash; 812 | } 813 | 814 | } // namespace detail 815 | } // namespace bev 816 | 817 | namespace std { 818 | 819 | // [string.view.hash], hash support: 820 | 821 | template 822 | struct hash> 823 | { 824 | size_t 825 | operator()(const bev::basic_string_view& str) const noexcept 826 | { return bev::detail::hash_bytes_(str.str_, str.length()*sizeof(CharT)); } 827 | }; 828 | 829 | } // namespace std 830 | -------------------------------------------------------------------------------- /test/CMakeLists.txt: -------------------------------------------------------------------------------- 1 | cmake_minimum_required(VERSION 3.12) 2 | 3 | project(string_view_tests LANGUAGES CXX) 4 | 5 | # ---- Add root project ---- 6 | 7 | # Enable warnings from includes 8 | set(string_view_INCLUDE_WITHOUT_SYSTEM ON CACHE INTERNAL "") 9 | add_subdirectory("${PROJECT_SOURCE_DIR}/.." "${PROJECT_BINARY_DIR}/root_project") 10 | 11 | # ---- Test ---- 12 | 13 | enable_testing() 14 | 15 | add_executable(sv_test tests.cpp) 16 | 17 | target_link_libraries(sv_test PRIVATE bev::string_view) 18 | target_compile_features(sv_test PRIVATE cxx_std_17) 19 | 20 | add_test(NAME string_view.main COMMAND sv_test) 21 | # At the moment the test consists of returning a comparison result, which is 22 | # expected to be true, i.e. a non-zero result 23 | set_property(TEST string_view.main PROPERTY WILL_FAIL YES) 24 | -------------------------------------------------------------------------------- /test/tests.cpp: -------------------------------------------------------------------------------- 1 | #include 2 | 3 | int main() { 4 | // TODO: Somehow run the existing libstdc++ string_view test suite against this class. 5 | std::string foo("asdf"); 6 | bev::string_view sv{foo}; 7 | return foo == sv; 8 | } 9 | --------------------------------------------------------------------------------