If performance matters most, write your own specialized string processing code which works on "raw" data in memory buffers. If convenience matters look at https

If performance matters most, write your own specialized string processing code which works on "raw" data in memory buffers. If convenience matters look at https://github.com/fmtlib/fmt https://github.com/fmtlib/fmt (or std::format which AFAIK is less feature rich) and https://github.com/imageworks/pystring https://github.com/imageworks/pystring.