函数名: kbhit
功 能: 检查当前按下的键
用 法: int kbhit(void);
程序例:

#include <conio.h>

int main(void)
{
cprintf("Press any key to continue:");
while (!kbhit()) /* do nothing */ ;
cprintf("\r\nA key was pressed...\r\n");
return 0;
}

函数名: keep
功 能: 退出并继续驻留
用 法: void keep(int status, int size);
程序例:

/***NOTE:
This is an interrupt service routine. You
can NOT compile this program with Test
Stack Overflow turned on and get an
executable file which will operate
correctly. Due to the nature of this
function the formula used to compute
the number of paragraphs may not
necessarily work in all cases. Use with
care! Terminate Stay Resident (TSR)
programs are complex and no other support
for them is provided. Refer to the
MS-DOS technical documentation
for more information. */
#include <dos.h>
/* The clock tick interrupt */
#define INTR 0x1C
/* Screen attribute (blue on grey) */
#define ATTR 0x7900

/* reduce heaplength and stacklength
to make a smaller program in memory */
extern unsigned _heaplen = 1024;
extern unsigned _stklen = 512;

void interrupt ( *oldhandler)(void);

void interrupt handler(void)
{
unsigned int (far *screen)[80];
static int count;

/* For a color screen the video memory
is at B800:0000. For a monochrome
system use B000:000 */
screen = MK_FP(0xB800,0);

/* increase the counter and keep it
within 0 to 9 */
count++;
count %= 10;

/* put the number on the screen */
screen[0][79] = count + '0' + ATTR;

/* call the old interrupt handler */
oldhandler();
}

int main(void)
{

/* get the address of the current clock
tick interrupt */
oldhandler = getvect(INTR);

/* install the new interrupt handler */
setvect(INTR, handler);

/* _psp is the starting address of the
program in memory. The top of the stack
is the end of the program. Using _SS and
_SP together we can get the end of the
stack. You may want to allow a bit of
saftey space to insure that enough room
is being allocated ie:
(_SS + ((_SP + safety space)/16) - _psp)
*/
keep(0, (_SS + (_SP/16) - _psp));
return 0;
}

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