libstdc++
system_error
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1// <system_error> -*- C++ -*-
2
3// Copyright (C) 2007-2022 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file include/system_error
26 * This is a Standard C++ Library header.
27 */
28
29#ifndef _GLIBCXX_SYSTEM_ERROR
30#define _GLIBCXX_SYSTEM_ERROR 1
31
32#pragma GCC system_header
33
34#if __cplusplus < 201103L
35# include <bits/c++0x_warning.h>
36#else
37
38#include <bits/c++config.h>
39#include <bits/error_constants.h>
40#include <iosfwd>
41#include <stdexcept>
42#if __cplusplus > 201703L
43# include <compare>
44#endif
45
46namespace std _GLIBCXX_VISIBILITY(default)
47{
48_GLIBCXX_BEGIN_NAMESPACE_VERSION
49
50 /** @addtogroup diagnostics
51 * @{
52 */
53
54 class error_code;
55 class error_condition;
56 class system_error;
57
58 /// is_error_code_enum
59 template<typename _Tp>
60 struct is_error_code_enum : public false_type { };
61
62 /// is_error_condition_enum
63 template<typename _Tp>
64 struct is_error_condition_enum : public false_type { };
65
66 template<>
67 struct is_error_condition_enum<errc>
68 : public true_type { };
69
70#if __cplusplus > 201402L
71 template <typename _Tp>
72 inline constexpr bool is_error_code_enum_v =
73 is_error_code_enum<_Tp>::value;
74 template <typename _Tp>
75 inline constexpr bool is_error_condition_enum_v =
76 is_error_condition_enum<_Tp>::value;
77#endif // C++17
78 /// @}
79
80_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
81
82 /** @addtogroup diagnostics
83 * @{
84 */
85
86 /** Abstract base class for types defining a category of error codes.
87 *
88 * An error category defines a context that gives meaning to the integer
89 * stored in an `error_code` or `error_condition` object. For example,
90 * the standard `errno` constants such a `EINVAL` and `ENOMEM` are
91 * associated with the "generic" category and other OS-specific error
92 * numbers are associated with the "system" category, but a user-defined
93 * category might give different meanings to the same numerical values.
94 *
95 * A user-defined category can override the `equivalent` member functions
96 * to define correspondence between errors in different categories.
97 * For example, a category for errors from disk I/O could consider some
98 * of its error numbers equivalent to ENOSPC and ENOENT in the generic
99 * category.
100 *
101 * @headerfile system_error
102 * @since C++11
103 */
104 class error_category
105 {
106 public:
107 constexpr error_category() noexcept = default;
108
109 virtual ~error_category();
110
111 error_category(const error_category&) = delete;
112 error_category& operator=(const error_category&) = delete;
113
114 /// A string that identifies the error category.
115 virtual const char*
116 name() const noexcept = 0;
117
118 // We need two different virtual functions here, one returning a
119 // COW string and one returning an SSO string. Their positions in the
120 // vtable must be consistent for dynamic dispatch to work, but which one
121 // the name "message()" finds depends on which ABI the caller is using.
122#if _GLIBCXX_USE_CXX11_ABI
123 private:
124 _GLIBCXX_DEFAULT_ABI_TAG
125 virtual __cow_string
126 _M_message(int) const;
127
128 public:
129 /// A description of the error condition corresponding to the number.
130 _GLIBCXX_DEFAULT_ABI_TAG
131 virtual string
132 message(int) const = 0;
133#else
134 virtual string
135 message(int) const = 0;
136
137 private:
138 virtual __sso_string
139 _M_message(int) const;
140#endif
141
142 public:
143 /// Return an error_condition corresponding to `i` in this category.
144 virtual error_condition
145 default_error_condition(int __i) const noexcept;
146
147 /// Test whether `cond` corresponds to `i` for this category.
148 virtual bool
149 equivalent(int __i, const error_condition& __cond) const noexcept;
150
151 /// Test whether `code` corresponds to `i` for this category.
152 virtual bool
153 equivalent(const error_code& __code, int __i) const noexcept;
154
155 /// An error_category only compares equal to itself.
156 [[__nodiscard__]]
157 bool
158 operator==(const error_category& __other) const noexcept
159 { return this == &__other; }
160
161 /// Ordered comparison that defines a total order for error categories.
162#if __cpp_lib_three_way_comparison
163 [[nodiscard]]
164 strong_ordering
165 operator<=>(const error_category& __rhs) const noexcept
166 { return std::compare_three_way()(this, &__rhs); }
167#else
168 bool
169 operator<(const error_category& __other) const noexcept
170 { return less<const error_category*>()(this, &__other); }
171
172 bool
173 operator!=(const error_category& __other) const noexcept
174 { return this != &__other; }
175#endif
176 };
177
178 // DR 890.
179
180 /// Error category for `errno` error codes.
181 [[__nodiscard__, __gnu__::__const__]]
182 const error_category&
183 generic_category() noexcept;
184
185 /// Error category for other error codes defined by the OS.
186 [[__nodiscard__, __gnu__::__const__]]
187 const error_category&
188 system_category() noexcept;
189
190 /// @}
191
192_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
193
194 /** @addtogroup diagnostics
195 * @{
196 */
197
198namespace __adl_only
199{
200 void make_error_code() = delete;
201 void make_error_condition() = delete;
202}
203
204 /** Class error_code
205 *
206 * This class is a value type storing an integer error number and a
207 * category that gives meaning to the error number. Typically this is done
208 * close the the point where the error happens, to capture the original
209 * error value.
210 *
211 * An `error_code` object can be used to store the original error value
212 * emitted by some subsystem, with a category relevant to the subsystem.
213 * For example, errors from POSIX library functions can be represented by
214 * an `errno` value and the "generic" category, but errors from an HTTP
215 * library might be represented by an HTTP response status code (e.g. 404)
216 * and a custom category defined by the library.
217 *
218 * @headerfile system_error
219 * @since C++11
220 */
221 class error_code
222 {
223 public:
224 error_code() noexcept
225 : _M_value(0), _M_cat(&system_category()) { }
226
227 error_code(int __v, const error_category& __cat) noexcept
228 : _M_value(__v), _M_cat(&__cat) { }
229
230 template<typename _ErrorCodeEnum, typename = typename
231 enable_if<is_error_code_enum<_ErrorCodeEnum>::value>::type>
232 error_code(_ErrorCodeEnum __e) noexcept
233 {
234 using __adl_only::make_error_code;
235 *this = make_error_code(__e);
236 }
237
238 void
239 assign(int __v, const error_category& __cat) noexcept
240 {
241 _M_value = __v;
242 _M_cat = &__cat;
243 }
244
245 void
246 clear() noexcept
247 { assign(0, system_category()); }
248
249 // DR 804.
250 template<typename _ErrorCodeEnum>
251 typename enable_if<is_error_code_enum<_ErrorCodeEnum>::value,
252 error_code&>::type
253 operator=(_ErrorCodeEnum __e) noexcept
254 { return *this = make_error_code(__e); }
255
256 /// The error value.
257 [[__nodiscard__]]
258 int
259 value() const noexcept { return _M_value; }
260
261 /// The error category that this error belongs to.
262 [[__nodiscard__]]
263 const error_category&
264 category() const noexcept { return *_M_cat; }
265
266 /// An `error_condition` for this error's category and value.
267 error_condition
268 default_error_condition() const noexcept;
269
270 /// The category's description of the value.
271 _GLIBCXX_DEFAULT_ABI_TAG
272 string
273 message() const
274 { return category().message(value()); }
275
276 /// Test whether `value()` is non-zero.
277 [[__nodiscard__]]
278 explicit operator bool() const noexcept
279 { return _M_value != 0; }
280
281 // DR 804.
282 private:
283 int _M_value;
284 const error_category* _M_cat;
285 };
286
287 // C++11 19.5.2.5 non-member functions
288
289 /** Create an `error_code` representing a standard `errc` condition.
290 *
291 * The `std::errc` constants correspond to `errno` macros and so use the
292 * generic category.
293 *
294 * @relates error_code
295 * @since C++11
296 */
297 [[__nodiscard__]]
298 inline error_code
299 make_error_code(errc __e) noexcept
300 { return error_code(static_cast<int>(__e), generic_category()); }
301
302 /** Ordered comparison for std::error_code.
303 *
304 * This defines a total order by comparing the categories, and then
305 * if they are equal comparing the values.
306 *
307 * @relates error_code
308 * @since C++11
309 */
310#if __cpp_lib_three_way_comparison
311 [[nodiscard]]
312 inline strong_ordering
313 operator<=>(const error_code& __lhs, const error_code& __rhs) noexcept
314 {
315 if (auto __c = __lhs.category() <=> __rhs.category(); __c != 0)
316 return __c;
317 return __lhs.value() <=> __rhs.value();
318 }
319#else
320 inline bool
321 operator<(const error_code& __lhs, const error_code& __rhs) noexcept
322 {
323 return (__lhs.category() < __rhs.category()
324 || (__lhs.category() == __rhs.category()
325 && __lhs.value() < __rhs.value()));
326 }
327#endif
328
329 /** Write a std::error_code to an ostream.
330 *
331 * @relates error_code
332 * @since C++11
333 */
334 template<typename _CharT, typename _Traits>
335 basic_ostream<_CharT, _Traits>&
336 operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
337 { return (__os << __e.category().name() << ':' << __e.value()); }
338
339 /** Class error_condition
340 *
341 * This class represents error conditions that may be visible at an API
342 * boundary. Different `error_code` values that can occur within a library
343 * or module might map to the same `error_condition`.
344 *
345 * An `error_condition` represents something that the program can test for,
346 * and subsequently take appropriate action.
347 *
348 * @headerfile system_error
349 * @since C++11
350 */
351 class error_condition
352 {
353 public:
354 /// Initialize with a zero (no error) value and the generic category.
355 error_condition() noexcept
356 : _M_value(0), _M_cat(&generic_category()) { }
357
358 /// Initialize with the specified value and category.
359 error_condition(int __v, const error_category& __cat) noexcept
360 : _M_value(__v), _M_cat(&__cat) { }
361
362 template<typename _ErrorConditionEnum, typename = typename
363 enable_if<is_error_condition_enum<_ErrorConditionEnum>::value>::type>
364 error_condition(_ErrorConditionEnum __e) noexcept
365 {
366 using __adl_only::make_error_condition;
367 *this = make_error_condition(__e);
368 }
369
370 /// Set the value and category.
371 void
372 assign(int __v, const error_category& __cat) noexcept
373 {
374 _M_value = __v;
375 _M_cat = &__cat;
376 }
377
378 // DR 804.
379 template<typename _ErrorConditionEnum>
380 typename enable_if<is_error_condition_enum
381 <_ErrorConditionEnum>::value, error_condition&>::type
382 operator=(_ErrorConditionEnum __e) noexcept
383 { return *this = make_error_condition(__e); }
384
385 /// Reset the value and category to the default-constructed state.
386 void
387 clear() noexcept
388 { assign(0, generic_category()); }
389
390 // C++11 19.5.3.4 observers
391
392 /// The error value.
393 [[__nodiscard__]]
394 int
395 value() const noexcept { return _M_value; }
396
397 /// The error category that this error belongs to.
398 [[__nodiscard__]]
399 const error_category&
400 category() const noexcept { return *_M_cat; }
401
402 /// The category's description of the value.
403 _GLIBCXX_DEFAULT_ABI_TAG
404 string
405 message() const
406 { return category().message(value()); }
407
408 /// Test whether `value()` is non-zero.
409 [[__nodiscard__]]
410 explicit operator bool() const noexcept
411 { return _M_value != 0; }
412
413 // DR 804.
414 private:
415 int _M_value;
416 const error_category* _M_cat;
417 };
418
419 // C++11 19.5.3.5 non-member functions
420
421 /** Create an `error_condition` representing a standard `errc` condition.
422 *
423 * The `std::errc` constants correspond to `errno` macros and so use the
424 * generic category.
425 *
426 * @relates error_condition
427 * @since C++11
428 */
429 [[__nodiscard__]]
430 inline error_condition
431 make_error_condition(errc __e) noexcept
432 { return error_condition(static_cast<int>(__e), generic_category()); }
433
434 // C++11 19.5.4 Comparison operators
435
436 /** Equality comparison for std::error_code.
437 *
438 * Returns true only if they have the same category and the same value.
439 *
440 * @relates error_condition
441 * @since C++11
442 */
443 [[__nodiscard__]]
444 inline bool
445 operator==(const error_code& __lhs, const error_code& __rhs) noexcept
446 {
447 return __lhs.category() == __rhs.category()
448 && __lhs.value() == __rhs.value();
449 }
450
451 /** Equality comparison for std::error_code and std::error_condition.
452 *
453 * Uses each category's `equivalent` member function to check whether
454 * the values correspond to an equivalent error in that category.
455 *
456 * @relates error_condition
457 * @since C++11
458 */
459 [[__nodiscard__]]
460 inline bool
461 operator==(const error_code& __lhs, const error_condition& __rhs) noexcept
462 {
463 return __lhs.category().equivalent(__lhs.value(), __rhs)
464 || __rhs.category().equivalent(__lhs, __rhs.value());
465 }
466
467 /** Equality comparison for std::error_condition.
468 *
469 * Returns true only if they have the same category and the same value.
470 *
471 * @relates error_condition
472 * @since C++11
473 */
474 [[__nodiscard__]]
475 inline bool
476 operator==(const error_condition& __lhs,
477 const error_condition& __rhs) noexcept
478 {
479 return __lhs.category() == __rhs.category()
480 && __lhs.value() == __rhs.value();
481 }
482
483 /** Ordered comparison for std::error_condition.
484 *
485 * This defines a total order by comparing the categories, and then
486 * if they are equal comparing the values.
487 *
488 * @relates error_condition
489 * @since C++11
490 */
491#if __cpp_lib_three_way_comparison
492 [[nodiscard]]
493 inline strong_ordering
494 operator<=>(const error_condition& __lhs,
495 const error_condition& __rhs) noexcept
496 {
497 if (auto __c = __lhs.category() <=> __rhs.category(); __c != 0)
498 return __c;
499 return __lhs.value() <=> __rhs.value();
500 }
501#else
502 inline bool
503 operator<(const error_condition& __lhs,
504 const error_condition& __rhs) noexcept
505 {
506 return (__lhs.category() < __rhs.category()
507 || (__lhs.category() == __rhs.category()
508 && __lhs.value() < __rhs.value()));
509 }
510
511 /// @relates error_condition
512 inline bool
513 operator==(const error_condition& __lhs, const error_code& __rhs) noexcept
514 {
515 return (__rhs.category().equivalent(__rhs.value(), __lhs)
516 || __lhs.category().equivalent(__rhs, __lhs.value()));
517 }
518
519 /// @relates error_code
520 inline bool
521 operator!=(const error_code& __lhs, const error_code& __rhs) noexcept
522 { return !(__lhs == __rhs); }
523
524 /// @relates error_code
525 inline bool
526 operator!=(const error_code& __lhs, const error_condition& __rhs) noexcept
527 { return !(__lhs == __rhs); }
528
529 /// @relates error_condition
530 inline bool
531 operator!=(const error_condition& __lhs, const error_code& __rhs) noexcept
532 { return !(__lhs == __rhs); }
533
534 /// @relates error_condition
535 inline bool
536 operator!=(const error_condition& __lhs,
537 const error_condition& __rhs) noexcept
538 { return !(__lhs == __rhs); }
539#endif // three_way_comparison
540 /// @}
541
542 /**
543 * @brief An exception type that includes an `error_code` value.
544 *
545 * Typically used to report errors from the operating system and other
546 * low-level APIs.
547 *
548 * @headerfile system_error
549 * @since C++11
550 * @ingroup exceptions
551 */
552 class system_error : public std::runtime_error
553 {
554 private:
555 error_code _M_code;
556
557 public:
558 system_error(error_code __ec = error_code())
559 : runtime_error(__ec.message()), _M_code(__ec) { }
560
561 system_error(error_code __ec, const string& __what)
562 : runtime_error(__what + ": " + __ec.message()), _M_code(__ec) { }
563
564 system_error(error_code __ec, const char* __what)
565 : runtime_error(__what + (": " + __ec.message())), _M_code(__ec) { }
566
567 system_error(int __v, const error_category& __ecat, const char* __what)
568 : system_error(error_code(__v, __ecat), __what) { }
569
570 system_error(int __v, const error_category& __ecat)
571 : runtime_error(error_code(__v, __ecat).message()),
572 _M_code(__v, __ecat) { }
573
574 system_error(int __v, const error_category& __ecat, const string& __what)
575 : runtime_error(__what + ": " + error_code(__v, __ecat).message()),
576 _M_code(__v, __ecat) { }
577
578#if __cplusplus >= 201103L
579 system_error (const system_error &) = default;
580 system_error &operator= (const system_error &) = default;
581#endif
582
583 virtual ~system_error() noexcept;
584
585 const error_code&
586 code() const noexcept { return _M_code; }
587 };
588
589_GLIBCXX_END_NAMESPACE_VERSION
590} // namespace
591
592#include <bits/functional_hash.h>
593
594namespace std _GLIBCXX_VISIBILITY(default)
595{
596_GLIBCXX_BEGIN_NAMESPACE_VERSION
597
598#ifndef _GLIBCXX_COMPATIBILITY_CXX0X
599 // DR 1182.
600 /// std::hash specialization for error_code.
601 /// @relates error_code
602 template<>
603 struct hash<error_code>
604 : public __hash_base<size_t, error_code>
605 {
606 size_t
607 operator()(const error_code& __e) const noexcept
608 {
609 const size_t __tmp = std::_Hash_impl::hash(__e.value());
610 return std::_Hash_impl::__hash_combine(&__e.category(), __tmp);
611 }
612 };
613#endif // _GLIBCXX_COMPATIBILITY_CXX0X
614
615#if __cplusplus >= 201703L
616 // DR 2686.
617 /// std::hash specialization for error_condition.
618 /// @relates error_condition
619 template<>
620 struct hash<error_condition>
621 : public __hash_base<size_t, error_condition>
622 {
623 size_t
624 operator()(const error_condition& __e) const noexcept
625 {
626 const size_t __tmp = std::_Hash_impl::hash(__e.value());
627 return std::_Hash_impl::__hash_combine(&__e.category(), __tmp);
628 }
629 };
630#endif
631
632_GLIBCXX_END_NAMESPACE_VERSION
633} // namespace
634
635#endif // C++11
636
637#endif // _GLIBCXX_SYSTEM_ERROR