std::atomic<T>::operator++,++(int),--,--(int)
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Concurrency support library
Cooperative cancellation
Mutual exclusion Generic lock management
Condition variables Semaphores Latches and Barriers
Futures
Safe reclamation Hazard pointers
(C++11)
(C++20)
(C++11)
(C++11)
(C++20)
(C++26)
(C++26)
(C++20)
(C++26)
(C++20)
(C++26)
(C++26)
(C++26)
(C++26)
(C++26)
(C++26)
(C++11)
(C++11)
(C++17)
(C++11)
(C++14)
(C++11)
(C++11)
(C++11)
(C++11)(C++11)(C++11)(C++11)(C++11)(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++20)(C++20)
(C++20)
(C++20)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++26)
(C++26)
(C++26)
(C++11)
(C++20)
(C++11)
(C++11)(deprecated in C++20)
(C++11)(deprecated in C++20)
(C++11)
(C++11)
(C++11)(deprecated in C++26)
(C++11)
(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++11)(C++11)
(C++26)(C++26)
(C++26)(C++26)
(C++11)
(C++20)(C++20)
(C++20)
(C++20)
(C++11)(C++11)
(C++11)(C++11)
(C++20)(C++20)
(C++20)(C++20)
(C++20)
(C++20)
std::atomic
(C++20)
(C++20)
(C++20)
(C++17)
(C++26)
(C++26)
atomic::operator++atomic::operator++(int)atomic::operator--atomic::operator--(int)
member only of
atomic<Integral > specializationsT operator++() noexcept;
(1)
(since C++11)
T operator++() volatile noexcept;
(2)
(since C++11)
T operator++( int ) noexcept;
(3)
(since C++11)
T operator++( int ) volatile noexcept;
(4)
(since C++11)
T operator--() noexcept;
(5)
(since C++11)
T operator--() volatile noexcept;
(6)
(since C++11)
T operator--( int ) noexcept;
(7)
(since C++11)
T operator--( int ) volatile noexcept;
(8)
(since C++11)
member only of
atomic<T*> partial specializationT* operator++() noexcept;
(9)
(since C++11)
T* operator++() volatile noexcept;
(10)
(since C++11)
T* operator++( int ) noexcept;
(11)
(since C++11)
T* operator++( int ) volatile noexcept;
(12)
(since C++11)
T* operator--() noexcept;
(13)
(since C++11)
T* operator--() volatile noexcept;
(14)
(since C++11)
T* operator--( int ) noexcept;
(15)
(since C++11)
T* operator--( int ) volatile noexcept;
(16)
(since C++11)
Atomically increments or decrements the current value. The operation is read-modify-write operation.
- operator++() performs atomic pre-increment. Equivalent to return fetch_add(1) + 1;.
- operator++(int) performs atomic post-increment. Equivalent to return fetch_add(1);.
- operator--() performs atomic pre-decrement. Equivalent to return fetch_sub(1) - 1;.
- operator--(int) performs atomic post-decrement. Equivalent to return fetch_sub(1);.
1-8) For signed integral types, arithmetic is defined to use two’s complement representation. There are no undefined results.
9-16) The result may be an undefined address, but the operations otherwise have no undefined behavior.
If
T is not a complete object type, the program is ill-formed.It is deprecated if std::atomic <T>::is_always_lock_free is false and any volatile overload participates in overload resolution.
(since C++20)[edit] Return value
operator++() and operator--() return the value of the atomic variable after the modification. Formally, the result of incrementing/decrementing the value immediately preceding the effects of this function in the modification order of *this.
operator++(int) and operator--(int) return the value of the atomic variable before the modification. Formally, the value immediately preceding the effects of this function in the modification order of *this.
[edit] Notes
Unlike most pre-increment and pre-decrement operators, the pre-increment and pre-decrement operators for atomic types do not return a reference to the modified object. They return a copy of the stored value instead.
[edit] Example
Run this code
#include <atomic> #include <chrono> #include <iomanip> #include <iostream> #include <mutex> #include <random> #include <string> #include <thread> std::atomic <int> atomic_count{0}; std::mutex cout_mutex; int completed_writes{0}; constexpr int global_max_count{72}; constexpr int writes_per_line{8}; constexpr int max_delay{100}; template<int Max> int random_value() { static std::uniform_int_distribution <int> distr{1, Max}; static std::random_device engine; static std::mt19937 noise{engine()}; static std::mutex rand_mutex; std::lock_guard lock{rand_mutex}; return distr(noise); } int main() { auto work = [](const std::string id) { for (int count{}; (count = ++atomic_count) <= global_max_count;) { std::this_thread::sleep_for ( std::chrono::milliseconds (random_value<max_delay>())); // print thread `id` and `count` value { std::lock_guard lock{cout_mutex}; const bool new_line = ++completed_writes % writes_per_line == 0; std::cout << id << std::setw (3) << count << " " << (new_line ? "\n" : "") << std::flush ; } } }; std::jthread j1(work, "░"), j2(work, "▒"), j3(work, "▓"), j4(work, "█"); }
Possible output:
▒ 2 ░ 1 ▒ 5 ▒ 7 █ 4 ░ 6 ▓ 3 ▒ 8 ▓ 11 █ 9 ▓ 13 ░ 10 █ 14 ▒ 12 ░ 16 ░ 19 ▓ 15 ▒ 18 ▓ 21 ▒ 22 █ 17 █ 25 ▒ 24 █ 26 ░ 20 ░ 29 ▒ 27 ▓ 23 ▒ 31 ▒ 33 ▓ 32 █ 28 ░ 30 ░ 37 ▒ 34 ▓ 35 █ 36 █ 41 ▓ 40 ▒ 39 ░ 38 ▓ 43 █ 42 ▓ 46 ▓ 48 █ 47 █ 50 ░ 45 ▒ 44 ▒ 53 ▒ 54 ▓ 49 ▒ 55 █ 51 ▒ 57 █ 58 ░ 52 ▓ 56 ░ 61 ▒ 59 █ 60 ▓ 62 ▒ 64 ░ 63 ░ 68 ▓ 66 █ 65 █ 71 ▒ 67 ▓ 70 ░ 69 █ 72
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P0558R1 | C++11 | arithmetic permitted on pointers to (possibly cv-qualified) void or function | made ill-formed |
[edit] See also
atomically adds the argument to the value stored in the atomic object and obtains the value held previously
(public member function) [edit]
(public member function) [edit]
atomically subtracts the argument from the value stored in the atomic object and obtains the value held previously
(public member function) [edit]
(public member function) [edit]