atomic_load, atomic_load_explicit

Defined in header <stdatomic.h>
C atomic_load( const volatile A* obj );
(1) (since C11)
C atomic_load_explicit( const volatile A* obj, memory_order order );
(2) (since C11)

Atomically loads and returns the current value of the atomic variable pointed to by obj. The operation is atomic read operation.

The first version orders memory accesses according to memory_order_seq_cst, the second version orders memory accesses according to order. order must be one of memory_order_relaxed, memory_order_consume, memory_order_acquire or memory_order_seq_cst. Otherwise the behavior is undefined.

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 objects, and volatile semantic is preserved when applying this operation to volatile atomic objects. C is the non-atomic type corresponding to A.

It is unspecified whether the name of a generic function is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual function (e.g. parenthesized like (atomic_load)(...)), or a program defines an external identifier with the name of a generic function, the behavior is undefined.


obj - pointer to the atomic object to access
order - the memory synchronization ordering for this operation

Return value

The current value of the atomic variable pointed to by obj.


  • C17 standard (ISO/IEC 9899:2018):
    • The atomic_load generic functions (p: 206)
  • C11 standard (ISO/IEC 9899:2011):
    • The atomic_load generic functions (p: 282)

See also

stores a value in an atomic object
C++ documentation for atomic_load, atomic_load_explicit

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