# atomic_exchange, atomic_exchange_explicit

< c‎ | atomic
 Defined in header  C atomic_exchange( volatile A* obj, C desired ); (1) (since C11) C atomic_exchange_explicit( volatile A* obj, C desired, memory_order order ); (2) (since C11)

Atomically replaces the value pointed by obj with desired and returns the value obj held previously. The operation is read-modify-write operation. The first version orders memory accesses according to memory_order_seq_cst, the second version orders memory accesses according to order.

This is a generic function defined for all atomic object types A. The argument is pointer to a volatile atomic type to accept addresses of both non-volatile and volatile (e.g. memory-mapped I/O) atomic variables.C is the non-atomic type corresponding to A..

## Contents

### Parameters

 obj - pointer to the atomic object to modify desired - the value to replace the atomic object with order - the memory synchronization ordering for this operation: all values are permitted

### Return value

The value held previously be the atomic object pointed to by obj.

### References

• C11 standard (ISO/IEC 9899:2011):
• 7.17.7.3 The atomic_exchange generic functions (p: 283)