It's a simple, dumb, lightweight string builder implementation for those who have to work with C-style strings and won't link fat libraries.
The main version is a C++ class with a straighforward realisation and quite obvious interface. There is also a pure C, procedure-based verision, that is just a rewrite of original C++ class.
Just drop the files in your project. May be you'll need to do some edits to satisfy your compiler/IDE idiosyncrasies.
This code is licensed under WTFPL.