Simple C++ program to compare address and size of std::string instance and the c_str() pointer to see what is the maximum length of SSO (short string optimization - storing the data inside the std::string instance itself if its very small, to avoid using a dynamic allocation).

An instance of std::string commonly has a pointer to the string data, and a couple of integers (size and capacity), which adds up to 24 bytes on a 64-bit architecture. SSO takes advantage of the fact that many strings in common programs are small, and stores them inside those bytes themselves, instead of allocating memory on the heap. This also helps avoid a cache miss, but all this at the cost of some extra complexity (having to figure out and store flag to mark short vs. normal string).

• (video) CppCon 2016: Nicholas Ormrod - The strange details of std::string at Facebook
• SSO-23 - proof of concept string that uses all bytes for SSO
• Meaning of acronym SSO in the context of std::string
• How to Measure String SSO Length with constinit and constexpr

• 64-bit g++ 13 and MSVC 19:

sizeof(std::string) = 32
sizeof(void*) = 8
max SSO = 15

• 32-bit g++ 13 and MSVC 19:

sizeof(std::string) = 24
sizeof(void*) = 4
max SSO = 15

• 64-bit executable created by with zig c++:

sizeof(std::string) = 24
sizeof(void*) = 8
max SSO = 22