I think most(?) C++ implementations of std::string use something called a short-string optimization, where the string type is something like struct string {

I think most(?) C++ implementations of std::string use something called a short-string optimization, where the string type is something like struct string { size_t len; union { char* ptr_to_malloced_string; char short_string[sizeof(char*)]; } } So if the length of the string is shorter than the size of a pointer, the string is stored inline in the struct, and if the length is longer it's a separate allocated object.