What are the "serious" libraries?

[Joe Nelson]

There are also those libraries which provide strings that keep track of
their length with a number rather than relying on \0 termination. I've
always shied away from this kind of thing since I don't use standard
library functions that could overflow, but I did find this comparison
interesting:

http://bstring.sourceforge.net/features.html

It identifies libsrt as a runner up to bstring. What's interesting about
libsrt is that it includes more than just strings -- namely vector, bit
set, set, map, hash set, and hash map.

https://github.com/faragon/libsrt

It's fairly new, but looks thorough and tested.