函数名:setactivepage

功 能: 设置图形输出活动页

用 法: void far setactivepage(int pagenum);

程序例:

#include <graphics.h>

#include <stdlib.h>

#include <stdio.h>

#include <conio.h>

int main(void)

{

/* select a driver and mode that supports */

/* multiple pages. */

int gdriver = EGA, gmode = EGAHI, errorcode;

int x, y, ht;

/* initialize graphics and local variables */

initgraph(&gdriver, &gmode, "");

/* read result of initialization */

errorcode = graphresult();

if (errorcode != grOk) /* an error occurred */

{

printf("Graphics error: %s\", grapherrormsg(errorcode));

printf("Press any key to halt:");

getch();

exit(1); /* terminate with an error code */

}

x = getmaxx() / 2;

y = getmaxy() / 2;

ht = textheight("W");

/* select the off screen page for drawing */

setactivepage(1);

/* draw a line on page #1 */

line(0, 0, getmaxx(), getmaxy());

/* output a message on page #1 */

settextjustify(CENTER_TEXT, CENTER_TEXT);

outtextxy(x, y, "This is page #1:");

outtextxy(x, y+ht, "Press any key to halt:");

/* select drawing to page #0 */

setactivepage(0);

/* output a message on page #0 */

outtextxy(x, y, "This is page #0.");

outtextxy(x, y+ht, "Press any key to view page #1:");

getch();

/* select page #1 as the visible page */

setvisualpage(1);

/* clean up */

getch();

closegraph();

return 0;

}