The std::to_address, introduced in C++20, is used to obtain the address represented by the specified pointer without forming a reference to the pointee. The existing std::addressof cannot do std::addressof(*ptr) because *ptr isn’t always an object. The std::to_address solves these issues for us.
Syntax:
template class Ptr constexpr auto to_address(const Ptr& p) noexcept; template class T constexpr T* to_address(T* p) noexcept;
Parameters: This method accepts a parameter p which is the fancy or raw pointer whose address is to be found.
Return value: This method returns the Raw pointer that represents the address of pointer p.
Below examples demonstrate the use of std::address
Example 1:
// C++ code to show // the use of std::address #include <iostream> #include <memory> using namespace std;
// Allocate memory and return // the pointer to that memory template < class A>
auto allocator_new(A& a)
{ auto p = a.allocate(1);
try {
allocator_traits<A>::construct(
a, to_address(p));
}
catch (...) {
a.deallocate(p, 1);
throw ;
}
cout << "Pointer to Memory allocated: "
<< p << endl;
return p;
} // Delete memory using // pointer to that memory template < class A>
void allocator_delete(
A& a,
typename allocator_traits<A>::pointer p)
{ allocator_traits<A>::destroy(
a, to_address(p));
a.deallocate(p, 1);
cout << "Pointer to Memory deleted: "
<< p << endl;
} // Driver code int main()
{ allocator< int > a;
auto p = allocator_new(a);
allocator_delete(a, p);
} |
Output:
Pointer to Memory allocated: 0x1512c20 Pointer to Memory deleted: 0x1512c20
Example 2:
// C++ code to show // the use of std::address #include <iostream> #include <memory> using namespace std;
int main()
{ // Make a unique pointer and
// use to_address to get its address
// from heap memory
cout << "Using unique pointers\n\n" ;
auto ptr = make_unique< int >(15);
cout << "Address of pointer to 15: "
<< to_address(ptr) << "\n" ;
auto ptr1 = make_unique< int >(17);
cout << "Address of pointer to 17: "
<< to_address(ptr1) << "\n" ;
// Use to_address to get the
// address of a dumb pointer
// from stack memory
cout << "\nUsing dumb pointers\n\n" ;
int i = 17;
cout << "Address of pointer to 17: "
<< to_address(&i) << "\n" ;
int j = 18;
cout << "Address of pointer to 18: "
<< to_address(&j) << "\n" ;
return 0;
} |
Output:
Using unique pointers Address of pointer to 15: 0x181ec30 Address of pointer to 17: 0x181ec50 Using dumb pointers Address of pointer to 17: 0x7fff6b454398 Address of pointer to 18: 0x7fff6b45439c
Reference: https://en.cppreference.com/w/cpp/memory/to_address