int (*f_listen)(COMSTACK handle, char *addrp, int *addrlen);
COMSTACK (*f_accept)(COMSTACK handle);
int (*f_close)(COMSTACK handle);
int (*f_listen)(COMSTACK handle, char *addrp, int *addrlen);
COMSTACK (*f_accept)(COMSTACK handle);
int (*f_close)(COMSTACK handle);