函数名: setwritemode 
 功  能: 设置图形方式下画线的输出模式 
 用  法: #include <graphics.h> 
         void far setwritemode(int mode); 
 程序例: 
#include <graphics.h> 
 #include <stdlib.h> 
 #include <stdio.h> 
 #include <conio.h> 
int main() 
 { 
    /* request auto detection */ 
    int gdriver = DETECT, gmode, errorcode; 
    int xmax, ymax; 
   /* initialize graphics and local variables */ 
    initgraph(&gdriver, &gmode, ""); 
   /* read result of initialization */ 
    errorcode = graphresult(); 
    if (errorcode != grOk)  /* an error occurred */ 
    { 
       printf("Graphics error: %s\n", grapherrormsg(errorcode)); 
       printf("Press any key to halt:"); 
       getch(); 
       exit(1); /* terminate with an error code */ 
    } 
   xmax = getmaxx(); 
    ymax = getmaxy(); 
   /* select XOR drawing mode */ 
    setwritemode(XOR_PUT); 
   /* draw a line */ 
    line(0, 0, xmax, ymax); 
    getch(); 
   /* erase the line by drawing over it */ 
    line(0, 0, xmax, ymax); 
    getch(); 
   /* select overwrite drawing mode */ 
    setwritemode(COPY_PUT); 
   /* draw a line */ 
    line(0, 0, xmax, ymax); 
   /* clean up */ 
    getch(); 
    closegraph(); 
    return 0; 
 }