Cygwin's default person interface is the bash shell operating within the mintty terminal emulator.[25] The DLL also implements pseudo terminal (pty) devices, and Cygwin ships with numerous terminal emulators which are according to them, such as rxvt/urxvt and xterm. The version of GCC that comes with Cygwin has various extensions https://acgwin18418.blogsmine.com/37539912/what-does-acgwin-mean