函数名: coreleft 
 功  能: 返回未使用内存的大小 
 用  法: #include <alloc.h> 
         unsigned coreleft(void); 
 程序例: 
#include <stdio.h> 
 #include <alloc.h> 
int main(void) 
 { 
    printf("The difference between the highest allocated block and\n"); 
    printf("the top of the heap is: %lu bytes\n", (unsigned long) coreleft()); 
   return 0; 
 }