1. exit handler.unix
atexit(void (*func)(void)); #automatically called by exit()blog
exit() calls these functions in reverse order of their registeration. Ease function is called as many times as it was registered.ci
2. environment list get
extern char ** environit
access to specific environment variable, use getenv() and putenv()io
3. memory arragementfunction
unix command size report the size(in bytes) of the text , data and bss segmentsclass