我使用std::queue实现JobQueue类。(基本上这个类以FIFO方式处理每个作业)。 在一个场景中，我希望一次性清除队列(从队列中删除所有作业)。 我在std::queue类中没有看到任何可用的清除方法。
如何有效地实现JobQueue类的清除方法?
我有一个简单的解决方案弹出在一个循环，但我正在寻找更好的方法。
//Clears the job queue
void JobQueue ::clearJobs()
{
// I want to avoid pop in a loop
while (!m_Queue.empty())
{
m_Queue.pop();
}
}
当前回答
Author of the topic asked how to clear the queue "efficiently", so I assume he wants better complexity than linear O(queue size). Methods served by David Rodriguez, anon have the same complexity: according to STL reference, operator = has complexity O(queue size). IMHO it's because each element of queue is reserved separately and it isn't allocated in one big memory block, like in vector. So to clear all memory, we have to delete every element separately. So the straightest way to clear std::queue is one line:
while(!Q.empty()) Q.pop();
其他回答
清除标准容器的一个常用习语是交换容器的空版本:
void clear( std::queue<int> &q )
{
std::queue<int> empty;
std::swap( q, empty );
}
它也是清除某些容器内内存的唯一方法(std::vector)
我宁愿不依赖swap()或将队列设置为新创建的队列对象，因为队列元素没有正确地销毁。调用pop()调用各自元素对象的析构函数。这在<int>队列中可能不是问题，但可能会对包含对象的队列产生副作用。
因此，如果您想防止可能的副作用，那么使用while(!queue.empty()) queue.pop();进行循环似乎是最有效的解决方案，至少对于包含对象的队列是如此。
是的-有点队列类的错误特征，恕我直言。这就是我所做的:
#include <queue>
using namespace std;;
int main() {
queue <int> q1;
// stuff
q1 = queue<int>();
}
Author of the topic asked how to clear the queue "efficiently", so I assume he wants better complexity than linear O(queue size). Methods served by David Rodriguez, anon have the same complexity: according to STL reference, operator = has complexity O(queue size). IMHO it's because each element of queue is reserved separately and it isn't allocated in one big memory block, like in vector. So to clear all memory, we have to delete every element separately. So the straightest way to clear std::queue is one line:
while(!Q.empty()) Q.pop();
您可以创建一个继承自队列的类，并直接清除底层容器。这是非常有效的。
template<class T>
class queue_clearable : public std::queue<T>
{
public:
void clear()
{
c.clear();
}
};
也许你的a实现也允许你的Queue对象(这里是JobQueue)继承std:: Queue <Job>，而不是将Queue作为成员变量。这样就可以在成员函数中直接访问c.clear()。
