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# C++ STL源码剖析之容器配接器stack与queue、priority_queue
## 0.导语
为何stack与queue不被称为容器呢？
下面本节带着这个问题来深入源码分析。
## 1.stack
在stack的源码中我们关注两点：
- 默认`_Sequence`为`deque`
- 内部函数实现是调用`_Sequence`对应容器的函数。
![stack.png](https://raw.githubusercontent.com/Light-City/cloudimg/master/stack.png)
```cpp
template<typename _Tp, typename _Sequence = deque<_Tp> >
class stack
{
public:
typedef typename _Sequence::value_type value_type;
typedef typename _Sequence::reference reference;
typedef typename _Sequence::const_reference const_reference;
typedef typename _Sequence::size_type size_type;
typedef _Sequence container_type;
protected:
// See queue::c for notes on this name.
_Sequence c;
public:
reference
top()
{
__glibcxx_requires_nonempty();
return c.back();
}
void
push(const value_type& __x)
{ c.push_back(__x); }
}
```
> 测试stack底层容器
对于stack来说，底层容器可以是`vector`、`deque`、`list`，但不可以是`map`、`set`。
由于编译器不会做全面性检查，当调用函数不存在的时候，就编译不通过，所以对于像set虽然不能作为底层容器，但如果具有某些函数，调用仍然是成功的，直到调用的函数不存在。
```cpp
int test_stack() {
cout<<"============test_stack============="<<endl;
clock_t timeStart = clock();
stack<int, list<int>> c;
for (long i = 0; i < 100000; i++)
c.push(i+1);
cout << "stack.size()= " << c.size() << endl;
cout << "stack.top()= " << c.top() << endl;
c.pop();
cout << "stack.size()= " << c.size() << endl;
cout << "stack.top()= " << c.top() << endl;
cout << "use stack milli-seconds : " << (clock() - timeStart) << endl;
timeStart=clock();
stack<int, deque<int>> c1;
for (long i = 0; i < 100000; i++)
c1.push(i+1);
cout << "stack.size()= " << c1.size() << endl;
cout << "stack.top()= " << c1.top() << endl;
c1.pop();
cout << "stack.size()= " << c1.size() << endl;
cout << "stack.top()= " << c1.top() << endl;
cout << "use stack milli-seconds : " << (clock() - timeStart) << endl;
// vector可以作为stack的底层容器
stack<int, vector<int>> c2;
for (long i = 0; i < 100000; i++)
c2.push(i+1);
cout << "stack.size()= " << c2.size() << endl;
cout << "stack.top()= " << c2.top() << endl;
c2.pop();
cout << "stack.size()= " << c2.size() << endl;
cout << "stack.top()= " << c2.top() << endl;
cout << "use stack milli-seconds : " << (clock() - timeStart) << endl;
}
```
## 2.queue
在queue的源码中我们关注两点：
- 默认`_Sequence`为`deque`
- 内部函数实现是调用`_Sequence`对应容器的函数。
```cpp
template<typename _Tp, typename _Sequence = deque<_Tp> >
class queue
{
public:
typedef typename _Sequence::value_type value_type;
typedef typename _Sequence::reference reference;
typedef typename _Sequence::const_reference const_reference;
typedef typename _Sequence::size_type size_type;
typedef _Sequence container_type;
protected:
_Sequence c;
public:
void push(const value_type& __x)
{ c.push_back(__x); }
void pop()
{
__glibcxx_requires_nonempty();
c.pop_front();
}
}
```
其对应的UML类图如下：
![queue_.png](https://raw.githubusercontent.com/Light-City/cloudimg/master/queue_.png)
同理，优先队列则是使用`vector`作为默认容器。
```cpp
template<typename _Tp, typename _Sequence = vector<_Tp>,
typename _Compare = less<typename _Sequence::value_type> >
class priority_queue
{
public:
typedef typename _Sequence::value_type value_type;
typedef typename _Sequence::reference reference;
typedef typename _Sequence::const_reference const_reference;
typedef typename _Sequence::size_type size_type;
typedef _Sequence container_type;
protected:
// See queue::c for notes on these names.
_Sequence c;
_Compare comp;
public:
reference
top()
{
__glibcxx_requires_nonempty();
return c.front();
}
void
push(const value_type& __x)
{
c.push_back(__x);
std::push_heap(c.begin(), c.end(), comp);
}
}
```
![priority_queue.png](https://raw.githubusercontent.com/Light-City/cloudimg/master/priority_queue.png)
测试这两个容器配接器支持的底层容器：
> queue
对于queue底层容器可以是`deque`，也可以是`list`，但不能是`vector`,`map`,`set`，使用默认的deque效率在插入方面比其他容器作为底层要快！
```cpp
int test_queue() {
cout<<"============test_queue============="<<endl;
clock_t timeStart = clock();
queue<int, list<int>> c;
for (long i = 0; i < 100000; i++) {
c.push(i+1);
}
cout << "stack.size()= " << c.size() << endl;
cout << "stack.front()= " << c.front() << endl;
c.pop();
cout << "stack.size()= " << c.size() << endl;
cout << "stack.front()= " << c.front() << endl;
cout << "use list milli-seconds : " << (clock() - timeStart) << endl;
timeStart=clock();
queue<int, deque<int>> c1;
for (long i = 0; i < 100000; i++) {
c1.push(i+1);
}
cout << "stack.size()= " << c1.size() << endl;
cout << "stack.front()= " << c1.front() << endl;
c1.pop();
cout << "stack.size()= " << c1.size() << endl;
cout << "stack.front()= " << c1.front() << endl;
cout << "use deque milli-seconds : " << (clock() - timeStart) << endl;
}
```
> priority_queue
对于优先队列来说，测试结果发现，采用`deque`要比默认的`vector`插入速度快！
底层支持vector、deque容器，但不支持list、map、set。
```cpp
int test_priority_queue() {
cout<<"============test_priority_queue============="<<endl;
clock_t timeStart = clock();
priority_queue<int, deque<int>> c1;
for (long i = 0; i < 100000; i++) {
c1.push(i+1);
}
cout << "stack.size()= " << c1.size() << endl;
cout << "stack.top()= " << c1.top() << endl;
c1.pop();
cout << "stack.size()= " << c1.size() << endl;
cout << "stack.top()= " << c1.top() << endl;
cout << "use deque milli-seconds : " << (clock() - timeStart) << endl;
priority_queue<int, vector<int>> c2;
for (long i = 0; i < 100000; i++)
c2.push(i+1);
cout << "stack.size()= " << c2.size() << endl;
cout << "stack.top()= " << c2.top() << endl;
c2.pop();
cout << "stack.size()= " << c2.size() << endl;
cout << "stack.top()= " << c2.top() << endl;
cout << "use stack milli-seconds : " << (clock() - timeStart) << endl;
}
```
因此，stack、queue、priority_queue不被称为容器， 把它称为容器配接器。