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572 lines
21 KiB
C++
572 lines
21 KiB
C++
//
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// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// File: string_view.h
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// -----------------------------------------------------------------------------
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//
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// This file contains the definition of the `absl::string_view` class. A
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// `string_view` points to a contiguous span of characters, often part or all of
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// another `std::string`, double-quoted string literal, character array, or even
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// another `string_view`.
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//
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// This `absl::string_view` abstraction is designed to be a drop-in
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// replacement for the C++17 `std::string_view` abstraction.
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#ifndef ABSL_STRINGS_STRING_VIEW_H_
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#define ABSL_STRINGS_STRING_VIEW_H_
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#include <algorithm>
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#include "absl/base/config.h"
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#ifdef ABSL_HAVE_STD_STRING_VIEW
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#include <string_view>
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namespace absl {
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inline namespace lts_2018_12_18 {
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using std::string_view;
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} // inline namespace lts_2018_12_18
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} // namespace absl
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#else // ABSL_HAVE_STD_STRING_VIEW
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#include <cassert>
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#include <cstddef>
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#include <cstring>
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#include <iosfwd>
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#include <iterator>
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#include <limits>
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#include <string>
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#include "absl/base/internal/throw_delegate.h"
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#include "absl/base/macros.h"
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#include "absl/base/port.h"
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namespace absl {
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inline namespace lts_2018_12_18 {
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// absl::string_view
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//
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// A `string_view` provides a lightweight view into the string data provided by
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// a `std::string`, double-quoted string literal, character array, or even
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// another `string_view`. A `string_view` does *not* own the string to which it
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// points, and that data cannot be modified through the view.
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//
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// You can use `string_view` as a function or method parameter anywhere a
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// parameter can receive a double-quoted string literal, `const char*`,
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// `std::string`, or another `absl::string_view` argument with no need to copy
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// the string data. Systematic use of `string_view` within function arguments
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// reduces data copies and `strlen()` calls.
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//
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// Because of its small size, prefer passing `string_view` by value:
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//
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// void MyFunction(absl::string_view arg);
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//
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// If circumstances require, you may also pass one by const reference:
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//
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// void MyFunction(const absl::string_view& arg); // not preferred
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//
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// Passing by value generates slightly smaller code for many architectures.
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//
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// In either case, the source data of the `string_view` must outlive the
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// `string_view` itself.
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//
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// A `string_view` is also suitable for local variables if you know that the
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// lifetime of the underlying object is longer than the lifetime of your
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// `string_view` variable. However, beware of binding a `string_view` to a
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// temporary value:
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//
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// // BAD use of string_view: lifetime problem
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// absl::string_view sv = obj.ReturnAString();
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//
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// // GOOD use of string_view: str outlives sv
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// std::string str = obj.ReturnAString();
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// absl::string_view sv = str;
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//
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// Due to lifetime issues, a `string_view` is sometimes a poor choice for a
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// return value and usually a poor choice for a data member. If you do use a
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// `string_view` this way, it is your responsibility to ensure that the object
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// pointed to by the `string_view` outlives the `string_view`.
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//
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// A `string_view` may represent a whole string or just part of a string. For
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// example, when splitting a string, `std::vector<absl::string_view>` is a
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// natural data type for the output.
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//
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//
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// When constructed from a source which is nul-terminated, the `string_view`
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// itself will not include the nul-terminator unless a specific size (including
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// the nul) is passed to the constructor. As a result, common idioms that work
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// on nul-terminated strings do not work on `string_view` objects. If you write
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// code that scans a `string_view`, you must check its length rather than test
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// for nul, for example. Note, however, that nuls may still be embedded within
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// a `string_view` explicitly.
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//
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// You may create a null `string_view` in two ways:
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//
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// absl::string_view sv();
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// absl::string_view sv(nullptr, 0);
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//
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// For the above, `sv.data() == nullptr`, `sv.length() == 0`, and
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// `sv.empty() == true`. Also, if you create a `string_view` with a non-null
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// pointer then `sv.data() != nullptr`. Thus, you can use `string_view()` to
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// signal an undefined value that is different from other `string_view` values
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// in a similar fashion to how `const char* p1 = nullptr;` is different from
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// `const char* p2 = "";`. However, in practice, it is not recommended to rely
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// on this behavior.
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//
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// Be careful not to confuse a null `string_view` with an empty one. A null
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// `string_view` is an empty `string_view`, but some empty `string_view`s are
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// not null. Prefer checking for emptiness over checking for null.
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//
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// There are many ways to create an empty string_view:
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//
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// const char* nullcp = nullptr;
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// // string_view.size() will return 0 in all cases.
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// absl::string_view();
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// absl::string_view(nullcp, 0);
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// absl::string_view("");
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// absl::string_view("", 0);
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// absl::string_view("abcdef", 0);
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// absl::string_view("abcdef" + 6, 0);
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//
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// All empty `string_view` objects whether null or not, are equal:
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//
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// absl::string_view() == absl::string_view("", 0)
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// absl::string_view(nullptr, 0) == absl::string_view("abcdef"+6, 0)
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class string_view {
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public:
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using traits_type = std::char_traits<char>;
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using value_type = char;
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using pointer = char*;
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using const_pointer = const char*;
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using reference = char&;
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using const_reference = const char&;
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using const_iterator = const char*;
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using iterator = const_iterator;
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using const_reverse_iterator = std::reverse_iterator<const_iterator>;
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using reverse_iterator = const_reverse_iterator;
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using size_type = size_t;
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using difference_type = std::ptrdiff_t;
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static constexpr size_type npos = static_cast<size_type>(-1);
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// Null `string_view` constructor
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constexpr string_view() noexcept : ptr_(nullptr), length_(0) {}
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// Implicit constructors
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template <typename Allocator>
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string_view( // NOLINT(runtime/explicit)
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const std::basic_string<char, std::char_traits<char>, Allocator>&
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str) noexcept
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: ptr_(str.data()), length_(CheckLengthInternal(str.size())) {}
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// Implicit constructor of a `string_view` from nul-terminated `str`. When
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// accepting possibly null strings, use `absl::NullSafeStringView(str)`
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// instead (see below).
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#if ABSL_HAVE_BUILTIN(__builtin_strlen) || \
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(defined(__GNUC__) && !defined(__clang__))
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// GCC has __builtin_strlen according to
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// https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Other-Builtins.html, but
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// ABSL_HAVE_BUILTIN doesn't detect that, so we use the extra checks above.
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// __builtin_strlen is constexpr.
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constexpr string_view(const char* str) // NOLINT(runtime/explicit)
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: ptr_(str),
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length_(CheckLengthInternal(str ? __builtin_strlen(str) : 0)) {}
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#else
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constexpr string_view(const char* str) // NOLINT(runtime/explicit)
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: ptr_(str), length_(CheckLengthInternal(str ? strlen(str) : 0)) {}
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#endif
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// Implicit constructor of a `string_view` from a `const char*` and length.
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constexpr string_view(const char* data, size_type len)
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: ptr_(data), length_(CheckLengthInternal(len)) {}
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// NOTE: Harmlessly omitted to work around gdb bug.
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// constexpr string_view(const string_view&) noexcept = default;
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// string_view& operator=(const string_view&) noexcept = default;
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// Iterators
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// string_view::begin()
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//
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// Returns an iterator pointing to the first character at the beginning of the
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// `string_view`, or `end()` if the `string_view` is empty.
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constexpr const_iterator begin() const noexcept { return ptr_; }
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// string_view::end()
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//
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// Returns an iterator pointing just beyond the last character at the end of
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// the `string_view`. This iterator acts as a placeholder; attempting to
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// access it results in undefined behavior.
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constexpr const_iterator end() const noexcept { return ptr_ + length_; }
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// string_view::cbegin()
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//
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// Returns a const iterator pointing to the first character at the beginning
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// of the `string_view`, or `end()` if the `string_view` is empty.
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constexpr const_iterator cbegin() const noexcept { return begin(); }
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// string_view::cend()
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//
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// Returns a const iterator pointing just beyond the last character at the end
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// of the `string_view`. This pointer acts as a placeholder; attempting to
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// access its element results in undefined behavior.
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constexpr const_iterator cend() const noexcept { return end(); }
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// string_view::rbegin()
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//
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// Returns a reverse iterator pointing to the last character at the end of the
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// `string_view`, or `rend()` if the `string_view` is empty.
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const_reverse_iterator rbegin() const noexcept {
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return const_reverse_iterator(end());
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}
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// string_view::rend()
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//
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// Returns a reverse iterator pointing just before the first character at the
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// beginning of the `string_view`. This pointer acts as a placeholder;
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// attempting to access its element results in undefined behavior.
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const_reverse_iterator rend() const noexcept {
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return const_reverse_iterator(begin());
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}
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// string_view::crbegin()
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//
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// Returns a const reverse iterator pointing to the last character at the end
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// of the `string_view`, or `crend()` if the `string_view` is empty.
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const_reverse_iterator crbegin() const noexcept { return rbegin(); }
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// string_view::crend()
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//
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// Returns a const reverse iterator pointing just before the first character
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// at the beginning of the `string_view`. This pointer acts as a placeholder;
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// attempting to access its element results in undefined behavior.
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const_reverse_iterator crend() const noexcept { return rend(); }
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// Capacity Utilities
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// string_view::size()
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//
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// Returns the number of characters in the `string_view`.
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constexpr size_type size() const noexcept {
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return length_;
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}
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// string_view::length()
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//
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// Returns the number of characters in the `string_view`. Alias for `size()`.
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constexpr size_type length() const noexcept { return size(); }
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// string_view::max_size()
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//
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// Returns the maximum number of characters the `string_view` can hold.
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constexpr size_type max_size() const noexcept { return kMaxSize; }
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// string_view::empty()
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//
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// Checks if the `string_view` is empty (refers to no characters).
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constexpr bool empty() const noexcept { return length_ == 0; }
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// std::string:view::operator[]
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//
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// Returns the ith element of an `string_view` using the array operator.
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// Note that this operator does not perform any bounds checking.
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constexpr const_reference operator[](size_type i) const { return ptr_[i]; }
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// string_view::front()
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//
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// Returns the first element of a `string_view`.
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constexpr const_reference front() const { return ptr_[0]; }
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// string_view::back()
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//
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// Returns the last element of a `string_view`.
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constexpr const_reference back() const { return ptr_[size() - 1]; }
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// string_view::data()
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//
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// Returns a pointer to the underlying character array (which is of course
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// stored elsewhere). Note that `string_view::data()` may contain embedded nul
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// characters, but the returned buffer may or may not be nul-terminated;
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// therefore, do not pass `data()` to a routine that expects a nul-terminated
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// std::string.
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constexpr const_pointer data() const noexcept { return ptr_; }
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// Modifiers
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// string_view::remove_prefix()
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//
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// Removes the first `n` characters from the `string_view`. Note that the
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// underlying std::string is not changed, only the view.
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void remove_prefix(size_type n) {
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assert(n <= length_);
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ptr_ += n;
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length_ -= n;
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}
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// string_view::remove_suffix()
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//
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// Removes the last `n` characters from the `string_view`. Note that the
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// underlying std::string is not changed, only the view.
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void remove_suffix(size_type n) {
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assert(n <= length_);
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length_ -= n;
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}
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// string_view::swap()
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//
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// Swaps this `string_view` with another `string_view`.
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void swap(string_view& s) noexcept {
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auto t = *this;
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*this = s;
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s = t;
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}
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// Explicit conversion operators
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// Converts to `std::basic_string`.
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template <typename A>
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explicit operator std::basic_string<char, traits_type, A>() const {
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if (!data()) return {};
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return std::basic_string<char, traits_type, A>(data(), size());
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}
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// string_view::copy()
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//
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// Copies the contents of the `string_view` at offset `pos` and length `n`
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// into `buf`.
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size_type copy(char* buf, size_type n, size_type pos = 0) const;
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// string_view::substr()
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//
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// Returns a "substring" of the `string_view` (at offset `pos` and length
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// `n`) as another string_view. This function throws `std::out_of_bounds` if
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// `pos > size`.
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string_view substr(size_type pos, size_type n = npos) const {
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if (ABSL_PREDICT_FALSE(pos > length_))
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base_internal::ThrowStdOutOfRange("absl::string_view::substr");
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n = std::min(n, length_ - pos);
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return string_view(ptr_ + pos, n);
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}
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// string_view::compare()
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//
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// Performs a lexicographical comparison between the `string_view` and
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// another `absl::string_view`, returning -1 if `this` is less than, 0 if
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// `this` is equal to, and 1 if `this` is greater than the passed std::string
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// view. Note that in the case of data equality, a further comparison is made
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// on the respective sizes of the two `string_view`s to determine which is
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// smaller, equal, or greater.
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int compare(string_view x) const noexcept {
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auto min_length = std::min(length_, x.length_);
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if (min_length > 0) {
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int r = memcmp(ptr_, x.ptr_, min_length);
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if (r < 0) return -1;
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if (r > 0) return 1;
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}
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if (length_ < x.length_) return -1;
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if (length_ > x.length_) return 1;
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return 0;
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}
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// Overload of `string_view::compare()` for comparing a substring of the
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// 'string_view` and another `absl::string_view`.
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int compare(size_type pos1, size_type count1, string_view v) const {
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return substr(pos1, count1).compare(v);
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}
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// Overload of `string_view::compare()` for comparing a substring of the
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// `string_view` and a substring of another `absl::string_view`.
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int compare(size_type pos1, size_type count1, string_view v, size_type pos2,
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size_type count2) const {
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return substr(pos1, count1).compare(v.substr(pos2, count2));
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}
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// Overload of `string_view::compare()` for comparing a `string_view` and a
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// a different C-style std::string `s`.
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int compare(const char* s) const { return compare(string_view(s)); }
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// Overload of `string_view::compare()` for comparing a substring of the
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// `string_view` and a different std::string C-style std::string `s`.
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int compare(size_type pos1, size_type count1, const char* s) const {
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return substr(pos1, count1).compare(string_view(s));
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}
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// Overload of `string_view::compare()` for comparing a substring of the
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// `string_view` and a substring of a different C-style std::string `s`.
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int compare(size_type pos1, size_type count1, const char* s,
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size_type count2) const {
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return substr(pos1, count1).compare(string_view(s, count2));
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}
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// Find Utilities
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// string_view::find()
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//
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// Finds the first occurrence of the substring `s` within the `string_view`,
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// returning the position of the first character's match, or `npos` if no
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// match was found.
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size_type find(string_view s, size_type pos = 0) const noexcept;
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// Overload of `string_view::find()` for finding the given character `c`
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// within the `string_view`.
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size_type find(char c, size_type pos = 0) const noexcept;
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// string_view::rfind()
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//
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// Finds the last occurrence of a substring `s` within the `string_view`,
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// returning the position of the first character's match, or `npos` if no
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// match was found.
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size_type rfind(string_view s, size_type pos = npos) const
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noexcept;
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// Overload of `string_view::rfind()` for finding the last given character `c`
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// within the `string_view`.
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size_type rfind(char c, size_type pos = npos) const noexcept;
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// string_view::find_first_of()
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//
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// Finds the first occurrence of any of the characters in `s` within the
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// `string_view`, returning the start position of the match, or `npos` if no
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// match was found.
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size_type find_first_of(string_view s, size_type pos = 0) const
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noexcept;
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// Overload of `string_view::find_first_of()` for finding a character `c`
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// within the `string_view`.
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size_type find_first_of(char c, size_type pos = 0) const
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noexcept {
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return find(c, pos);
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}
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// string_view::find_last_of()
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//
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// Finds the last occurrence of any of the characters in `s` within the
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// `string_view`, returning the start position of the match, or `npos` if no
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// match was found.
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size_type find_last_of(string_view s, size_type pos = npos) const
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noexcept;
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// Overload of `string_view::find_last_of()` for finding a character `c`
|
|
// within the `string_view`.
|
|
size_type find_last_of(char c, size_type pos = npos) const
|
|
noexcept {
|
|
return rfind(c, pos);
|
|
}
|
|
|
|
// string_view::find_first_not_of()
|
|
//
|
|
// Finds the first occurrence of any of the characters not in `s` within the
|
|
// `string_view`, returning the start position of the first non-match, or
|
|
// `npos` if no non-match was found.
|
|
size_type find_first_not_of(string_view s, size_type pos = 0) const noexcept;
|
|
|
|
// Overload of `string_view::find_first_not_of()` for finding a character
|
|
// that is not `c` within the `string_view`.
|
|
size_type find_first_not_of(char c, size_type pos = 0) const noexcept;
|
|
|
|
// string_view::find_last_not_of()
|
|
//
|
|
// Finds the last occurrence of any of the characters not in `s` within the
|
|
// `string_view`, returning the start position of the last non-match, or
|
|
// `npos` if no non-match was found.
|
|
size_type find_last_not_of(string_view s,
|
|
size_type pos = npos) const noexcept;
|
|
|
|
// Overload of `string_view::find_last_not_of()` for finding a character
|
|
// that is not `c` within the `string_view`.
|
|
size_type find_last_not_of(char c, size_type pos = npos) const
|
|
noexcept;
|
|
|
|
private:
|
|
static constexpr size_type kMaxSize =
|
|
(std::numeric_limits<difference_type>::max)();
|
|
|
|
static constexpr size_type CheckLengthInternal(size_type len) {
|
|
return ABSL_ASSERT(len <= kMaxSize), len;
|
|
}
|
|
|
|
const char* ptr_;
|
|
size_type length_;
|
|
};
|
|
|
|
// This large function is defined inline so that in a fairly common case where
|
|
// one of the arguments is a literal, the compiler can elide a lot of the
|
|
// following comparisons.
|
|
inline bool operator==(string_view x, string_view y) noexcept {
|
|
auto len = x.size();
|
|
if (len != y.size()) {
|
|
return false;
|
|
}
|
|
return x.data() == y.data() || len <= 0 ||
|
|
memcmp(x.data(), y.data(), len) == 0;
|
|
}
|
|
|
|
inline bool operator!=(string_view x, string_view y) noexcept {
|
|
return !(x == y);
|
|
}
|
|
|
|
inline bool operator<(string_view x, string_view y) noexcept {
|
|
auto min_size = std::min(x.size(), y.size());
|
|
const int r = min_size == 0 ? 0 : memcmp(x.data(), y.data(), min_size);
|
|
return (r < 0) || (r == 0 && x.size() < y.size());
|
|
}
|
|
|
|
inline bool operator>(string_view x, string_view y) noexcept { return y < x; }
|
|
|
|
inline bool operator<=(string_view x, string_view y) noexcept {
|
|
return !(y < x);
|
|
}
|
|
|
|
inline bool operator>=(string_view x, string_view y) noexcept {
|
|
return !(x < y);
|
|
}
|
|
|
|
// IO Insertion Operator
|
|
std::ostream& operator<<(std::ostream& o, string_view piece);
|
|
|
|
} // inline namespace lts_2018_12_18
|
|
} // namespace absl
|
|
|
|
#endif // ABSL_HAVE_STD_STRING_VIEW
|
|
|
|
namespace absl {
|
|
inline namespace lts_2018_12_18 {
|
|
|
|
// ClippedSubstr()
|
|
//
|
|
// Like `s.substr(pos, n)`, but clips `pos` to an upper bound of `s.size()`.
|
|
// Provided because std::string_view::substr throws if `pos > size()`
|
|
inline string_view ClippedSubstr(string_view s, size_t pos,
|
|
size_t n = string_view::npos) {
|
|
pos = std::min(pos, static_cast<size_t>(s.size()));
|
|
return s.substr(pos, n);
|
|
}
|
|
|
|
// NullSafeStringView()
|
|
//
|
|
// Creates an `absl::string_view` from a pointer `p` even if it's null-valued.
|
|
// This function should be used where an `absl::string_view` can be created from
|
|
// a possibly-null pointer.
|
|
inline string_view NullSafeStringView(const char* p) {
|
|
return p ? string_view(p) : string_view();
|
|
}
|
|
|
|
} // inline namespace lts_2018_12_18
|
|
} // namespace absl
|
|
|
|
#endif // ABSL_STRINGS_STRING_VIEW_H_
|