# std::atomic_ref<T>::fetch_sub

member only of `atomic_ref<` and `atomic_ref<` template specializations |
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T fetch_sub( T arg, std::memory_order order = std::memory_order_seq_cst ) const noexcept; |
(1) | |

member only of `atomic_ref<T*>` template specialization |
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T* fetch_sub( std::ptrdiff_t arg, std::memory_order order = std::memory_order_seq_cst ) const noexcept; |
(2) | |

Atomically replaces the current value of the referenced object with the result of arithmetic subtraction of the value and `arg`

. This operation is a 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.

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 of the referenced object, immediately preceding the effects of this function.

### Example

This section is incomplete Reason: no example |