summaryrefslogtreecommitdiff
path: root/absl/strings/string_view.h
blob: bd894e1daa4d6d8ea8fc07d48260cef3b8b4ca7c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
//
// 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_