相信大家对优先队列不陌生。

STL提供的PriorityQueue属于容器适配器，底层默认用vector容器来实现。实现原理是在用vector里构造一个

Heap(堆)，堆一般是用数组来储存的。

下面是一个使用有限队列的例子，用来实现一个错误关联器，总是把优先级高的错误放在最前面。

#include <string>

#include <queue>

#include <ostream>

#include <stdexcept>

// this class is implemented as inline.

// since it is just very simple

class Error

{

public:

Error(const std::string& e, int p) : errormessage(e), priority(p) {}

std::string GetErrorMessage() const { return errormessage;}

int GetPriority() const { return priority;}

void SetErrorMessage(const std::string& s) { errormessage = s;}

void SetPriority(int p) { priority = p; }

friend bool operator<(const Error& lhs, const Error& rhs); 

friend std::ostream& operator<<(std::ostream& out, const Error& e);

private:

std::string errormessage;

int priority;

};

 

class ErrorCorrector

{

public:

ErrorCorrector() {};

// add an error to the queue

void AddError(const Error& e);

// get error

Error GetError();

bool IsEmpty() const { return mErrors.empty();}

private:

std::priority_queue<Error>  mErrors;

ErrorCorrector(const ErrorCorrector&);

ErrorCorrector& operator=(const ErrorCorrector&);

};

 

实现:

#include "PriorityError.h"

std::ostream& operator<<(std::ostream& out, const Error& e )

{

out << e.priority << ": " << e.errormessage << std::endl;

return out;

}

void ErrorCorrector::AddError( const Error& e )

{

   mErrors.push(e);

}

Error ErrorCorrector::GetError()

{

  if (mErrors.empty())

  {

    throw std::out_of_range("the error is not empty");

  }

 

  Error e = mErrors.top();

  mErrors.pop();

  return  e;

}

bool operator<( const Error& lhs, const Error& rhs )

{

  return lhs.priority < rhs.priority;

}