一个有意思的C++泛型比较技巧文章

//2006-8-23 18:44  李国帅于网络收集

除了我感慨的编程者的技能之外，并无其他。
里面使用了构造函数，stl，泛型，重载运算符等技巧，虽然都是入门级技巧，不过能把它们灵活运用到一起实现一定目的，已经相当不容易。
/**

* Example of Comparator, with rectangles.
*/
#include <stdio.h>
#include <stdlib.h>

#include <iostream>
#include <vector>
using namespace std;

/**
* A simple rectangle class.
*/
class Rectangle
{
public:
//explicit用来防止由构造函数定义的隐式转换。
explicit Rectangle(int len = 0, int wid = 0)
: length(len), width(wid) { }

int getLength() const
{
return length;
}

int getWidth() const
{
return width;
}

void print(ostream & out = cout) const
{
out << "Rectangle " << getLength() << " by " << getWidth();
}

private:
int length;
int width;
};

ostream & operator<< (ostream & out, const Rectangle & rhs)
{
rhs.print(out);
return out;
}

/**
* Compare object: ordering by length.
*/
class LessThanByLength
{
public:
bool operator( ) (const Rectangle & lhs, const Rectangle & rhs) const
{

return lhs.getLength() < rhs.getLength();
}
};

/**
* Compare object: ordering by area.
*/
class LessThanByArea
{
public:
bool operator() (const Rectangle & lhs, const Rectangle & rhs) const
{
return lhs.getLength() * lhs.getWidth() < rhs.getLength() * rhs.getWidth();
}
};

/**
* Generic findMax, with a function object.
* Precondition: a.size( ) > 0.
*/
template <class Object, class Comparator>
const Object & findMax(const vector<Object> & a, Comparator isLessThan)
{
int maxIndex = 0;

for (int i = 1; i < a.size(); i++)
if (isLessThan(a[maxIndex], a[i]))
maxIndex = i;

return a[maxIndex];
}

/**
* main: create four rectangles.
* find the max, two ways
*/
int main()
{
vector<Rectangle> a;

a.push_back(Rectangle(1, 10));
a.push_back(Rectangle(10, 1));
a.push_back(Rectangle(5, 5));
a.push_back(Rectangle(4, 6));

//这是我添加的//
cout << "push rectangles:" << endl;
for (vector<Rectangle>::iterator it = a.begin(); it != a.end(); it++){
it->print(); cout << endl;
}

cout << "Largest length:\n\t" << findMax(a, LessThanByLength()) << endl;
cout << "Largest area:\n\t" << findMax(a, LessThanByArea()) << endl;

getchar();
return 0;
}