std::atomic<T>::fetch_sub
member only of atomic<Integral> (C++11) and atomic<Floating> (C++20) template specializations |
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(1) | ||
T fetch_sub( T arg, std::memory_order order = std::memory_order_seq_cst ) noexcept; |
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T fetch_sub( T arg, std::memory_order order = std::memory_order_seq_cst ) volatile noexcept; |
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member only of atomic<T*> template specialization |
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(2) | ||
T* fetch_sub( std::ptrdiff_t arg, std::memory_order order = std::memory_order_seq_cst ) noexcept; |
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T* fetch_sub( std::ptrdiff_t arg, std::memory_order order = std::memory_order_seq_cst ) volatile noexcept; |
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Atomically replaces the current value with the result of arithmetic subtraction of the value and arg
. The operation is read-modify-write operation. Memory is affected according to the value of order
.
For signed Integral
types, arithmetic is defined to use two’s complement representation. There are no undefined results.
For floating-point types, the floating-point environment in effect may be different from the calling thread's floating-point environment. The operation need not be conform to the corresponding std::numeric_limits traits but is encouraged to do so. If the result is not a representable value for its type, the result is unspecified but the operation otherwise has no undefined behavior. |
(since C++20) |
For T*
types, the result may be an undefined address, but the operation otherwise has no undefined behavior. The program is ill-formed if T
is not an object type.
Parameters
arg | - | the other argument of arithmetic subtraction |
order | - | memory order constraints to enforce |
Return value
The value immediately preceding the effects of this function in the modification order of *this
.
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 cv void or function | made ill-formed |
See also
(C++11)(C++11) |
subtracts a non-atomic value from an atomic object and obtains the previous value of the atomic (function template) |