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Abseil Team Export of internal Abseil changes. bf29470 Mar 20, 2019
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//
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// File: string_view.h
// -----------------------------------------------------------------------------
//
// This file contains the definition of the `absl::string_view` class. A
// `string_view` points to a contiguous span of characters, often part or all of
// another `std::string`, double-quoted string literal, character array, or even
// another `string_view`.
//
// This `absl::string_view` abstraction is designed to be a drop-in
// replacement for the C++17 `std::string_view` abstraction.
#ifndef ABSL_STRINGS_STRING_VIEW_H_
#define ABSL_STRINGS_STRING_VIEW_H_
#include <algorithm>
#include "absl/base/config.h"
#ifdef ABSL_HAVE_STD_STRING_VIEW
#include <string_view> // IWYU pragma: export
namespace absl {
using std::string_view;
} // namespace absl
#else // ABSL_HAVE_STD_STRING_VIEW
#include <cassert>
#include <cstddef>
#include <cstring>
#include <iosfwd>
#include <iterator>
#include <limits>
#include <string>
#include "absl/base/internal/throw_delegate.h"
#include "absl/base/macros.h"
#include "absl/base/port.h"
namespace absl {
// absl::string_view
//
// A `string_view` provides a lightweight view into the string data provided by
// a `std::string`, double-quoted string literal, character array, or even
// another `string_view`. A `string_view` does *not* own the string to which it
// points, and that data cannot be modified through the view.
//
// You can use `string_view` as a function or method parameter anywhere a
// parameter can receive a double-quoted string literal, `const char*`,
// `std::string`, or another `absl::string_view` argument with no need to copy
// the string data. Systematic use of `string_view` within function arguments
// reduces data copies and `strlen()` calls.
//
// Because of its small size, prefer passing `string_view` by value:
//
// void MyFunction(absl::string_view arg);
//
// If circumstances require, you may also pass one by const reference:
//
// void MyFunction(const absl::string_view& arg); // not preferred
//
// Passing by value generates slightly smaller code for many architectures.
//
// In either case, the source data of the `string_view` must outlive the
// `string_view` itself.
//
// A `string_view` is also suitable for local variables if you know that the
// lifetime of the underlying object is longer than the lifetime of your
// `string_view` variable. However, beware of binding a `string_view` to a
// temporary value:
//
// // BAD use of string_view: lifetime problem
// absl::string_view sv = obj.ReturnAString();
//
// // GOOD use of string_view: str outlives sv
// std::string str = obj.ReturnAString();
// absl::string_view sv = str;
//
// Due to lifetime issues, a `string_view` is sometimes a poor choice for a
// return value and usually a poor choice for a data member. If you do use a
// `string_view` this way, it is your responsibility to ensure that the object
// pointed to by the `string_view` outlives the `string_view`.
//
// A `string_view` may represent a whole string or just part of a string. For
// example, when splitting a string, `std::vector<absl::string_view>` is a
// natural data type for the output.
//
// When constructed from a source which is nul-terminated, the `string_view`
// itself will not include the nul-terminator unless a specific size (including
// the nul) is passed to the constructor. As a result, common idioms that work
// on nul-terminated strings do not work on `string_view` objects. If you write
// code that scans a `string_view`, you must check its length rather than test
// for nul, for example. Note, however, that nuls may still be embedded within
// a `string_view` explicitly.
//
// You may create a null `string_view` in two ways:
//
// absl::string_view sv();
// absl::string_view sv(nullptr, 0);
//
// For the above, `sv.data() == nullptr`, `sv.length() == 0`, and
// `sv.empty() == true`. Also, if you create a `string_view` with a non-null
// pointer then `sv.data() != nullptr`. Thus, you can use `string_view()` to
// signal an undefined value that is different from other `string_view` values
// in a similar fashion to how `const char* p1 = nullptr;` is different from
// `const char* p2 = "";`. However, in practice, it is not recommended to rely
// on this behavior.
//
// Be careful not to confuse a null `string_view` with an empty one. A null
// `string_view` is an empty `string_view`, but some empty `string_view`s are
// not null. Prefer checking for emptiness over checking for null.
//
// There are many ways to create an empty string_view:
//
// const char* nullcp = nullptr;
// // string_view.size() will return 0 in all cases.
// absl::string_view();
// absl::string_view(nullcp, 0);
// absl::string_view("");
// absl::string_view("", 0);
// absl::string_view("abcdef", 0);
// absl::string_view("abcdef" + 6, 0);
//
// All empty `string_view` objects whether null or not, are equal:
//
// absl::string_view() == absl::string_view("", 0)
// absl::string_view(nullptr, 0) == absl::string_view("abcdef"+6, 0)
class string_view {
public:
using traits_type = std::char_traits<char>;
using value_type = char;
using pointer = char*;
using const_pointer = const char*;
using reference = char&;
using const_reference = const char&;
using const_iterator = const char*;
using iterator = const_iterator;
using const_reverse_iterator = std::reverse_iterator<const_iterator>;
using reverse_iterator = const_reverse_iterator;
using size_type = size_t;
using difference_type = std::ptrdiff_t;
static constexpr size_type npos = static_cast<size_type>(-1);
// Null `string_view` constructor
constexpr string_view() noexcept : ptr_(nullptr), length_(0) {}
// Implicit constructors
template <typename Allocator>
string_view( // NOLINT(runtime/explicit)
const std::basic_string<char, std::char_traits<char>, Allocator>&
str) noexcept
: ptr_(str.data()), length_(CheckLengthInternal(str.size())) {}
// Implicit constructor of a `string_view` from nul-terminated `str`. When
// accepting possibly null strings, use `absl::NullSafeStringView(str)`
// instead (see below).
#if ABSL_HAVE_BUILTIN(__builtin_strlen) || \
(defined(__GNUC__) && !defined(__clang__))
// GCC has __builtin_strlen according to
// https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Other-Builtins.html, but
// ABSL_HAVE_BUILTIN doesn't detect that, so we use the extra checks above.
// __builtin_strlen is constexpr.
constexpr string_view(const char* str) // NOLINT(runtime/explicit)
: ptr_(str),
length_(CheckLengthInternal(str ? __builtin_strlen(str) : 0)) {}
#else
constexpr string_view(const char* str) // NOLINT(runtime/explicit)
: ptr_(str), length_(CheckLengthInternal(str ? strlen(str) : 0)) {}
#endif
// Implicit constructor of a `string_view` from a `const char*` and length.
constexpr string_view(const char* data, size_type len)
: ptr_(data), length_(CheckLengthInternal(len)) {}
// NOTE: Harmlessly omitted to work around gdb bug.
// constexpr string_view(const string_view&) noexcept = default;
// string_view& operator=(const string_view&) noexcept = default;
// Iterators
// string_view::begin()
//
// Returns an iterator pointing to the first character at the beginning of the
// `string_view`, or `end()` if the `string_view` is empty.
constexpr const_iterator begin() const noexcept { return ptr_; }
// string_view::end()
//
// Returns an iterator pointing just beyond the last character at the end of
// the `string_view`. This iterator acts as a placeholder; attempting to
// access it results in undefined behavior.
constexpr const_iterator end() const noexcept { return ptr_ + length_; }
// string_view::cbegin()
//
// Returns a const iterator pointing to the first character at the beginning
// of the `string_view`, or `end()` if the `string_view` is empty.
constexpr const_iterator cbegin() const noexcept { return begin(); }
// string_view::cend()
//
// Returns a const iterator pointing just beyond the last character at the end
// of the `string_view`. This pointer acts as a placeholder; attempting to
// access its element results in undefined behavior.
constexpr const_iterator cend() const noexcept { return end(); }
// string_view::rbegin()
//
// Returns a reverse iterator pointing to the last character at the end of the
// `string_view`, or `rend()` if the `string_view` is empty.
const_reverse_iterator rbegin() const noexcept {
return const_reverse_iterator(end());
}
// string_view::rend()
//
// Returns a reverse iterator pointing just before the first character at the
// beginning of the `string_view`. This pointer acts as a placeholder;
// attempting to access its element results in undefined behavior.
const_reverse_iterator rend() const noexcept {
return const_reverse_iterator(begin());
}
// string_view::crbegin()
//
// Returns a const reverse iterator pointing to the last character at the end
// of the `string_view`, or `crend()` if the `string_view` is empty.
const_reverse_iterator crbegin() const noexcept { return rbegin(); }
// string_view::crend()
//
// Returns a const reverse iterator pointing just before the first character
// at the beginning of the `string_view`. This pointer acts as a placeholder;
// attempting to access its element results in undefined behavior.
const_reverse_iterator crend() const noexcept { return rend(); }
// Capacity Utilities
// string_view::size()
//
// Returns the number of characters in the `string_view`.
constexpr size_type size() const noexcept {
return length_;
}
// string_view::length()
//
// Returns the number of characters in the `string_view`. Alias for `size()`.
constexpr size_type length() const noexcept { return size(); }
// string_view::max_size()
//
// Returns the maximum number of characters the `string_view` can hold.
constexpr size_type max_size() const noexcept { return kMaxSize; }
// string_view::empty()
//
// Checks if the `string_view` is empty (refers to no characters).
constexpr bool empty() const noexcept { return length_ == 0; }
// string_view::operator[]
//
// Returns the ith element of an `string_view` using the array operator.
// Note that this operator does not perform any bounds checking.
constexpr const_reference operator[](size_type i) const { return ptr_[i]; }
// string_view::front()
//
// Returns the first element of a `string_view`.
constexpr const_reference front() const { return ptr_[0]; }
// string_view::back()
//
// Returns the last element of a `string_view`.
constexpr const_reference back() const { return ptr_[size() - 1]; }
// string_view::data()
//
// Returns a pointer to the underlying character array (which is of course
// stored elsewhere). Note that `string_view::data()` may contain embedded nul
// characters, but the returned buffer may or may not be nul-terminated;
// therefore, do not pass `data()` to a routine that expects a nul-terminated
// std::string.
constexpr const_pointer data() const noexcept { return ptr_; }
// Modifiers
// string_view::remove_prefix()
//
// Removes the first `n` characters from the `string_view`. Note that the
// underlying std::string is not changed, only the view.
void remove_prefix(size_type n) {
assert(n <= length_);
ptr_ += n;
length_ -= n;
}
// string_view::remove_suffix()
//
// Removes the last `n` characters from the `string_view`. Note that the
// underlying std::string is not changed, only the view.
void remove_suffix(size_type n) {
assert(n <= length_);
length_ -= n;
}
// string_view::swap()
//
// Swaps this `string_view` with another `string_view`.
void swap(string_view& s) noexcept {
auto t = *this;
*this = s;
s = t;
}
// Explicit conversion operators
// Converts to `std::basic_string`.
template <typename A>
explicit operator std::basic_string<char, traits_type, A>() const {
if (!data()) return {};
return std::basic_string<char, traits_type, A>(data(), size());
}
// string_view::copy()
//
// Copies the contents of the `string_view` at offset `pos` and length `n`
// into `buf`.
size_type copy(char* buf, size_type n, size_type pos = 0) const;
// string_view::substr()
//
// Returns a "substring" of the `string_view` (at offset `pos` and length
// `n`) as another string_view. This function throws `std::out_of_bounds` if
// `pos > size`.
string_view substr(size_type pos, size_type n = npos) const {
if (ABSL_PREDICT_FALSE(pos > length_))
base_internal::ThrowStdOutOfRange("absl::string_view::substr");
n = (std::min)(n, length_ - pos);
return string_view(ptr_ + pos, n);
}
// string_view::compare()
//
// Performs a lexicographical comparison between the `string_view` and
// another `absl::string_view`, returning -1 if `this` is less than, 0 if
// `this` is equal to, and 1 if `this` is greater than the passed std::string
// view. Note that in the case of data equality, a further comparison is made
// on the respective sizes of the two `string_view`s to determine which is
// smaller, equal, or greater.
int compare(string_view x) const noexcept {
auto min_length = (std::min)(length_, x.length_);
if (min_length > 0) {
int r = memcmp(ptr_, x.ptr_, min_length);
if (r < 0) return -1;
if (r > 0) return 1;
}
if (length_ < x.length_) return -1;
if (length_ > x.length_) return 1;
return 0;
}
// Overload of `string_view::compare()` for comparing a substring of the
// 'string_view` and another `absl::string_view`.
int compare(size_type pos1, size_type count1, string_view v) const {
return substr(pos1, count1).compare(v);
}
// Overload of `string_view::compare()` for comparing a substring of the
// `string_view` and a substring of another `absl::string_view`.
int compare(size_type pos1, size_type count1, string_view v, size_type pos2,
size_type count2) const {
return substr(pos1, count1).compare(v.substr(pos2, count2));
}
// Overload of `string_view::compare()` for comparing a `string_view` and a
// a different C-style std::string `s`.
int compare(const char* s) const { return compare(string_view(s)); }
// Overload of `string_view::compare()` for comparing a substring of the
// `string_view` and a different std::string C-style std::string `s`.
int compare(size_type pos1, size_type count1, const char* s) const {
return substr(pos1, count1).compare(string_view(s));
}
// Overload of `string_view::compare()` for comparing a substring of the
// `string_view` and a substring of a different C-style std::string `s`.
int compare(size_type pos1, size_type count1, const char* s,
size_type count2) const {
return substr(pos1, count1).compare(string_view(s, count2));
}
// Find Utilities
// string_view::find()
//
// Finds the first occurrence of the substring `s` within the `string_view`,
// returning the position of the first character's match, or `npos` if no
// match was found.
size_type find(string_view s, size_type pos = 0) const noexcept;
// Overload of `string_view::find()` for finding the given character `c`
// within the `string_view`.
size_type find(char c, size_type pos = 0) const noexcept;
// string_view::rfind()
//
// Finds the last occurrence of a substring `s` within the `string_view`,
// returning the position of the first character's match, or `npos` if no
// match was found.
size_type rfind(string_view s, size_type pos = npos) const
noexcept;
// Overload of `string_view::rfind()` for finding the last given character `c`
// within the `string_view`.
size_type rfind(char c, size_type pos = npos) const noexcept;
// string_view::find_first_of()
//
// Finds the first occurrence of any of the characters in `s` within the
// `string_view`, returning the start position of the match, or `npos` if no
// match was found.
size_type find_first_of(string_view s, size_type pos = 0) const
noexcept;
// Overload of `string_view::find_first_of()` for finding a character `c`
// within the `string_view`.
size_type find_first_of(char c, size_type pos = 0) const
noexcept {
return find(c, pos);
}
// string_view::find_last_of()
//
// Finds the last occurrence of any of the characters in `s` within the
// `string_view`, returning the start position of the match, or `npos` if no
// match was found.
size_type find_last_of(string_view s, size_type pos = npos) const
noexcept;
// 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);
} // namespace absl
#endif // ABSL_HAVE_STD_STRING_VIEW
namespace absl {
// 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();
}
} // namespace absl
#endif // ABSL_STRINGS_STRING_VIEW_H_
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