c++ 文件问题！ thinking in c++ 中的stash测试

#include <fstream>
#include <iostream>
#include <string>
using namespace std;
struct Stack {
struct Link {
void* data;
Link* next;
void initialize(void* dat, Link* nxt);
}* head;
void initialize();
void push(void* dat);
void* peek();
void* pop();
void cleanup();
};
void
Stack::Link::initialize(void* dat, Link* nxt) {
data = dat;
next = nxt;
}

void Stack::initialize() { head = 0; }

void Stack::push(void* dat) {
Link* newLink = new Link;
newLink->initialize(dat, head);
head = newLink;
}

void* Stack::peek() {
// require(head != 0, "Stack empty");
return head->data;
}

void* Stack::pop() {
if(head == 0) return 0;
void* result = head->data;
Link* oldHead = head;
head = head->next;
delete oldHead;