An (In-)Complete Guide to C++ Object Lifetimes

Jonathan Müller

⏱ 90 minute session
11:00-12:30, Thursday, 18th April 2024
A C++ program manipulate objects, but it is undefined behavior if you attempt to manipulate them while they are not alive. So let's do a deep dive into object lifetime.

When are objects created and when are they destroyed? How does temporary lifetime extension come into play and what changed there recently? What happens when you std::malloc memory and just pretend objects are there without creating anything? Or worse: You use mmap() to read shared memory. How do unions interact with constructors, strict aliasing, or the "common initial sequence"? What when you explicitly call the destructor and later re-use the same storage? What's the deal with std::launder, std::bit_cast, and std::start_lifetime_as?

We'll answer all of those questions and much more. We'll do that by looking at the C++ standard, old and new proposals, and compiler optimizations.

🏷 undefined behavior
🏷 objects
🏷 lifetime
🏷 standard

Jonathan Müller

Jonathan is a library developer at think-cell. In his spare time, he works on various C++ open source libraries for memory allocation, cache-friendly containers, or parsing. He also blogs at and is a member of the C++ standardization committee.