函数名: sbrk 
 功  能: 改变数据段空间位置 
 用  法: #include <alloc.h>
         char *sbrk(int incr); 
 程序例: 
#include <stdio.h> 
 #include <alloc.h> 
int main(void) 
 { 
    printf("Changing allocation with sbrk()\n"); 
    printf("Before sbrk() call: %lu bytes free\n", 
    (unsigned long) coreleft()); 
    sbrk(1000); 
    printf(" After sbrk() call: %lu bytes free\n", 
    (unsigned long) coreleft()); 
    return 0; 
 }