priority_queue详解

priority_queue是一个安排好的顺序存储的队列，队首是优先级最高的元素。

Template<class T , class Container = vector<T> , class compare = less<T>>

第一个参数是priority_queue保存的元素类型T，Container是配置的底层容器，priority_queue默认使用了底层容器vector，但也可以使用deque,但是绝对不能使用list，因为list是不能随机访问元素的。Less是一个类模板，支持两个类型为T的元素进行operator<运算，来进行比较。（比较后得到优先级）

优先级越大离队首越近；，通过top()方法可以返回队首元素的const&，

#include <iostream>
#include <queue>
class Error
{
public:
    Error(int priority,std::string errorString)
            :mPriority(priority),mErrorString(errorString)
    {}

    int getPriority(){return mPriority;}
    std::string getErrorString(){return mErrorString;}
    friend bool operator <(const Error& lhs , const Error &rhs);
    friend std::ostream &operator << (std::ostream &os, Error& rhs);
private:
    std::string mErrorString;
    int mPriority;
};
bool operator <(const Error& lhs , const Error &rhs)
{
    return lhs.mPriority < rhs.mPriority;
}

std::ostream &operator << (std::ostream &os,Error& rhs)
{
    os << rhs.getErrorString() << "priority : " << rhs.getPriority() << std::endl;
    return os;
}

class ErrorCorrelateor
{
public:
    void addError(const Error & error);
    Error getError();

private:
    std::priority_queue<Error> mError;
};

void ErrorCorrelateor::addError(const Error & error)
{
    mError.push(error);
}

Error ErrorCorrelateor::getError()
{
    if(mError.empty())
    {
        throw std::out_of_range("priority queue is empty
");
    } else
    {
        Error tempError = mError.top();
        mError.pop();
        return tempError;
    }
}


int main() {
    ErrorCorrelateor correlateor;
    correlateor.addError(Error(1,"Unable to read file"));
    correlateor.addError(Error(5,"Incorrect entry User"));
    correlateor.addError(Error(9,"Unable collacate memery"));
    correlateor.addError(Error(5,"Unable write file"));

    while(true)
    {
        try
        {
            Error ec = correlateor.getError();
            std::cout << ec ;
        }catch (const std::out_of_range&)
        {
            std::cout << "Finised Error correlatetor" << std::endl;
            break;
        }
    }
    return 0;
}

结果是：

Unable collacate memerypriority : 9
Incorrect entry Userpriority : 5
Unable write filepriority : 5
Unable to read filepriority : 1
Finised Error correlatetor