addressof

Addressof is a utility function in the C++ standard library that returns the actual memory address of an object, bypassing any overloaded operator& that may be defined for the object's type. It is provided as std::addressof in the header <memory> and was introduced with the C++11 standard. The function is constexpr and noexcept and takes a non-const lvalue reference to an object, returning a pointer to that object's type.

The primary purpose of addressof is to obtain the true address of an object when a class overloads operator&. If operator& is overloaded, the expression &object would invoke the overloaded operator, which might return something other than the object's address. std::addressof avoids this resolution, using a technique that combines casts to produce the actual address. This makes addressof a reliable tool for low-level programming tasks, including certain memory-management and move-semantics implementations, where knowing the precise object address is important.

Usage typically involves passing an lvalue object to std::addressof to obtain a T* pointer, as in:

auto p = std::addressof(obj);

Notes:

- The function requires a non-const lvalue; it does not accept a const T& directly. To use it with const objects, const_cast may be needed, though const-correct code should be carefully considered when doing so.

- addressof is commonly used in conjunction with move constructors, custom containers, and internal utilities that need the actual address to work with object lifetimes or to pass addresses to APIs that expect raw pointers.

Related topics include the built-in operator& behavior, and modern alternatives like std::to_address (C++20) for pointer-like types.