函数名: flushall 
 功  能: 清除所有缓冲区 
 用  法: #include <stdio.h> 
         int flushall(void); 
 程序例: 
#include <stdio.h>
int main(void) 
 { 
    FILE *stream; 
   /* create a file */ 
    stream = fopen("DUMMY.FIL", "w"); 
   /* flush all open streams */ 
    printf("%d streams were flushed.\n", 
    flushall()); 
   /* close the file */ 
    fclose(stream); 
    return 0; 
 }