This is one of those questions that keeps coming up... "What core/low-level libraries has Google released as open source?" As someone who works inside of Google, I already know a lot of them and when I work on external code (e.g. GDAL) I have to work extra hard because the tools I normally reach for are not there. One of those is the C++ strings substitute.h. I just went looking and found it:
The question then becomes, where do I find the latest open sourced version and how do I use it in a library that will be used by many other people such as GDAL or libais? I probably have to move it into a gdal or osgeo namespace or it's going to clash at link time. If it's just an end tool, there there is less worry.