[dnr]

Don't forget supporting small strings (<= 7 bytes) in the pointer itself using tag bits. No allocation or dereferencing required.

[habibur]

Microsoft's MFC used to do this in their first version. But later ditched it. Maybe they found it not worth the trouble of checking for this condition everywhere. Increase in code.

[gpderetta]

Thse days, in C++, this is routinely done in various std::string implementations (which are both null terminated and have a separate length). In fact the standard was updated to explicitly allow this.