std::to_address in C++ with Examples

Last Updated : 04 Apr, 2020

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