ifdef.h

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

/*
 *
 * Conditional compilation definitions needed in ifdef.c and postio.c.
 *
 */

#ifdef SYSV
#include <termio.h>

#ifdef DKSTREAMS
#include <sys/stream.h>
#include <sys/stropts.h>
#endif

#endif

#ifdef V9
#include <sys/filio.h>
#include <sys/ttyio.h>

extern int	tty_ld;
#endif

#ifdef BSD4_2
#include <sgtty.h>
#include <sys/time.h>
#include <errno.h>

#define FD_ZERO(s) (s) = 0
#define FD_SET(n,s) (s) |= 1 << (n)

extern int	errno;
#endif

#ifdef DKHOST
#include <dk.h>
#include <sysexits.h>

extern char	*dtnamer();
extern int	dkminor();
#endif

/*
 *
 * External variable declarations - most (if not all) are defined in postio.c and
 * needed by the routines in ifdef.c.
 *
 */

extern char	*line;			/* printer is on this line */
extern int	ttyi;			/* input */
extern int	ttyo;			/* and output file descriptors */
extern FILE	*fp_log;		/* just for DKHOST stuff */

extern char	mesg[];			/* exactly what came back on ttyi */
extern char	*endmesg;		/* one in front of last free slot in mesg */
extern int	next;			/* next character goes in mesg[next] */

extern short	baudrate;		/* printer is running at this speed */
extern int	stopbits;		/* and expects this many stop bits */
extern int	interactive;		/* TRUE for interactive mode */

extern int	whatami;		/* a READ or WRITE process - or both */
extern int	canread;		/* allows reads */
extern int	canwrite;		/* and writes if TRUE */