迭代器使用起来非常方便，其实背后做了大量的工作。它是容器类的一个内嵌类，管理着一个指向容器类元素的指针。
#include<iostream>
#include<string>
#include<assert.h>
using std::cout;
using std::endl;
using std::string;
struct TestType{
string word;
TestType(string str = "") : word(str){}
};
template<class T>
class Stack {
struct Link {
T data;
Link* next;
Link(T dat, Link* nxt)
: data(dat), next(nxt) {}
}* head;
public:
Stack() : head(0) {
cout << "Stack default contructor\n";
}
~Stack();
void push(const T& dat) {
cout << "Stack::" << __FUNCTION__ << "\n";
head = new Link(dat, head);
}
T& peek() const {
cout << "Stack::" << __FUNCTION__ << "\n";
assert(head);
return head->data;
}
T pop();
// Nested iterator class:
class iterator; // Declaration required
friend class iterator; // Make it a friend
class iterator { // Now define it
Stack::Link* p;
public:
iterator(const Stack<T>& tstack) : p(tstack.head) {
cout << "iterator::" << __FUNCTION__ << "(const Stack<T>& tstack)\n";
}
// Copy-constructor:
iterator(const iterator& it) : p(it.p) {
cout << "iterator::" << __FUNCTION__ << "(const iterator& it)\n";
}
// The end sentinel iterator:
iterator() : p(0) {
cout << "iterator::" << __FUNCTION__ << "()\n";
}
// operator++ returns boolean indicating end:
iterator& operator++() {
cout << "iterator::" << __FUNCTION__ << "()\n";
if(p)
p = p->next;
return *this;
}
iterator& operator++(int) {
cout << "iterator::" << __FUNCTION__ << "(int)\n";
return operator++();
}
// Pointer dereference operator:
T* operator->() const {
cout << "iterator::" << __FUNCTION__ << "\n";
assert(p);
return &(p->data);
}
T& operator*() const {
cout << "iterator::" << __FUNCTION__ << "\n";
assert(p);
return p->data;
}
// bool conversion for conditional test:
operator bool() const {
cout << "iterator::" << __FUNCTION__ << "\n";
return bool(p);
}
// Comparison to test for end:
bool operator==(const iterator&it) const {
cout << "iterator::" << __FUNCTION__ << "\n";
return p == it.p;
}
bool operator!=(const iterator&it) const {
cout << "iterator::" << __FUNCTION__ << "\n";
return p != it.p;
}
};
iterator begin() const {
cout << "Stack::" << __FUNCTION__ << "\n";
return iterator(*this);
}
iterator end() const {
cout << "Stack::" << __FUNCTION__ << "\n";
return iterator();
}
};
template<class T>
Stack<T>::~Stack() {
cout << "Stack::" << __FUNCTION__ << "\n";
while(head)
pop();
}
template<class T>
T Stack<T>::pop() {
cout << "Stack::" << __FUNCTION__ << "\n";
if(head == 0) return T();
T result = head->data;
Link* oldHead = head;
head = head->next;
delete oldHead;
return result;
}
int main() {
Stack<TestType> textlines;
textlines.push(TestType(string("I")));
textlines.push(TestType(string("love")));
textlines.push(TestType(string("you")));
// Use iterator to print lines from the list:
for(auto it = textlines.begin(); it != textlines.end(); it++){
//for(auto it = textlines.begin(); it; it++){
cout << it->word << endl;
cout << (*it).word << endl;
}
return 0;
}
