函数名: bdos 
 功  能: DOS系统调用 
 用  法: #include <dos.h>
         int bdos(int dosfun, unsigned dosdx, unsigned dosal); 
 程序例: 
#include <stdio.h> 
 #include <dos.h> 
/* Get current drive as 'A', 'B', ... */ 
 char current_drive(void) 
 { 
    char curdrive; 
   /* Get current disk as 0, 1, ... */ 
    curdrive = bdos(0x19, 0, 0); 
    return('A' + curdrive); 
 } 
int main(void) 
 { 
    printf("The current drive is %c:\n", current_drive()); 
    return 0; 
 }