# std::declare_reachable

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< cpp‎ | memory

Defined in header `<memory>` |  |
void declare_reachable( void* p ); |  | (since C++11) (removed in C++23)

Declares the object referenced by the pointer p reachable. Reachable objects will not be deleted by the garbage collector or considered to be a leak by a leak detector even if all pointers to it are destroyed. An object may be declared reachable multiple times, in which case multiple calls to std::undeclare_reachable would be needed to remove this property. For example, a XOR linked list needs to declare its nodes reachable if the implementation has garbage collection enabled.

### Parameters

p | - | a safely-derived pointer or a null pointer

### Return value

(none)

### Exceptions

May throw std::bad_alloc if the system cannot allocate memory required to track reachable objects.

### See also

undeclare_reachable (C++11)(removed in C++23) | declares that an object can be recycled (function template)

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