函数名: isatty 
 功  能: 检查设备类型 
 用  法: #include <io.h> 
         int isatty(int handle); 
 程序例: 
#include <stdio.h> 
 #include <io.h> 
int main(void) 
 { 
    int handle; 
   handle = fileno(stdprn); 
    if (isatty(handle)) 
       printf("Handle %d is a device type\n", handle); 
    else 
       printf("Handle %d isn't a device type\n", handle); 
    return 0; 
 }