std::numpunct(3cxx) on Linux
The text 16ccc5ebc7bd, as Debian 10 (Buster) shipped it.
Primary class template numpunct. This facet stores several pieces of information related to printing and scanning numbers, such as the decimal point character. It takes a template parameter specifying the char type. The numpunct facet is used by streams for many I/O operations involving numbers.