Defined in header <stdatomic.h>
void atomic_init( volatile A* obj, C desired );
(since C11)

Initializes the default-constructed atomic object obj with the value desired. The function is not atomic: concurrent access from another thread, even through an atomic operation, is a data race.

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_init)(...)), or a program defines an external identifier with the name of a generic function, the behavior is undefined.


obj - pointer to an atomic object to initialize
desired - the value to initialize atomic object with

Return value



  • C17 standard (ISO/IEC 9899:2018):
    • The atomic_init generic function (p: 201)
  • C11 standard (ISO/IEC 9899:2011):
    • The atomic_init generic function (p: 274-275)

See also

(C11)(deprecated in C17)(removed in C23)
initializes a new atomic object
(function macro)
C++ documentation for atomic_init

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.