c get datetime string

from https://stackoverflow.com/questions/3053999/c-convert-time-t-to-string-with-format-yyyy-mm-dd-hhmmss

char buff[20];
time_t now = time(NULL);
strftime(buff, 20, "%Y-%m-%d %H:%M:%S", localtime(&now));
printf("buff :%s \n", buff);