function template
<memory>
std::undeclare_reachable
template <class T> T* undeclare_reachable (T* p);
Undeclare pointer as reachable
Revokes a previous declaration of reachability for the object pointed by p, and returns a safely-derived pointer to it.
If declare_reachable was called multiple times for the object pointed by p, the object is considered reachable until undeclare_reachable is called the same number of times.
Parameters
- p
- A pointer pointing to an object previously declared as reachable with declare_reachable.
Return value
A safely-derived pointer pointing to p. This pointer is guaranteed to compare equal to p.
This function throws no exceptions.
Example
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// declare_reachable / undeclare_reachable example
#include <iostream>
#include <memory>
#include <cstdint>
int main() {
int * p = new int (1); // dynamic object
std::declare_reachable(p);
p = (int*)((std::uintptr_t)p ^ UINTPTR_MAX); // scrambling p
// dynamic object not reachable by any live safely-derived pointer
p = std::undeclare_reachable((int*)((std::uintptr_t)p ^ UINTPTR_MAX));
// p is back again a safely-derived pointer to the dynamic object
std::cout << "p: " << *p << '\n';
delete p;
return 0;
}
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Output: