C ++如何排序数组变量 [英] C++ how to sort an array variable

问题描述

我有一个父类调用

Shape

Shape有两个子呼叫

Shape got 2 child call

Square and Rectangle

Shape类有一个变量调用区，它是int类型

Shape class got a variable call area, which is of int type

所以我创建了一个对象Square，Rectangle像这样

So i created some object of Square, Rectangle like this

int main()
{
    Shape *shaped[100];

    //then i did some adding of object..
    int areaValue;
    areaValue=1;

    shaped[0] = new Rectangle();
    shaped[0]->setArea(areaValue);

    areaValue=7;
    shaped[1] = new Square();
    shaped[1]->setArea(areaValue);

    areaValue=5;
    shaped[2] = new Square();
    shaped[2]->setArea(areaValue);

    shapeCounter = 3;

    sort(shaped[0],shaped[2]);

    for (int i=0;i<shapeCounter;i++)
    {
        cout << shaped[i].getArea() << endl;
    }

}

我尝试按升序区但它不工作。

I try to sort by ascending area but it doesnt work. no position change, the area still in the same sequence.

感谢您的帮助！

更新：

我在Shape.cpp中进行了以下更改

I did the following changes at Shape.cpp

 bool Shape::orderByArea(const Shape* lhs, const shape* rhs)
    {
      return lhs->area() < rhs->area();
    }

然后在main.cpp我做了

Then at main.cpp I did this

std::sort(shaped, shaped + 3, orderByArea);

但是我得到一个错误，orderByArea未在此范围内声明。

however i get an error, orderByArea was not declared in this scope.

我尝试的另一件事是：
使用向量排序

Another thing i tried was: To sort using vector

在Shape.h

At Shape.h

public:

bool operator<const Shape& x) const
{
return area < x.area;
}

在main.cpp

vector<ShapeTwoD*> sortVector;
sortVector.clear();
sortVector.assign(shaped,shaped + shapeCounter);

sort(sortVector.begin(),sortVector.end());

for(int i=0;i<shapeCounter;i++)
{
cout << sortVector[i].toDisplay() << endl;
}

但是没有什么可以排序。我尝试做一个打印输出，它的位置是一样的。

But nothing seems sorted. I try do a printout its position is same.

更新：现在固定。排序是工作。非常感谢专家！

我有另一个问题是

Shape * shaped [100] ;

Shape *shaped[100];

如何复制

Shape *shaped[100];

到

vector<Shape> myVector;

而不是

vector<Shape*> myVector;

所以我可以使用正常的对象排序。

so i can use the normal object sort.

推荐答案

在你的代码中你是怎么期望编译器知道你想按区域排序，魔术？我建议读一本关于标准C ++库（又名STL）的书，它将解释如何做自定义排序。在你的代码中，你有一个指针数组，所以你应该写一个可以排序指针的函数。另外你的std :: sort的参数是错误的。你的数组从成形开始，结束于 shaped + 3 （因为数组中有三个元素） / p>

In your code how did you expect the compiler to know that you wanted to sort by area, magic? I would recommend reading a book on the standard C++ library (aka the STL), it will explain how to do custom sorting. In your code you have an array of pointers, so you should write a functor that can order your pointers. Also your parameters to std::sort are wrong. Your array starts at shaped, and ends at shaped + 3 (since you have three elements in your array).

struct sort_by_area
{
    static bool operator()(Shape* x, Shape* y)
    {
        return x->getArea() < y->getArea();
    }
};

sort(shaped, shaped + 3, sort_by_area());

未经测试的代码，表示任何错误。

Untested code, apologies for any mistakes.

或者你可以使用一个函数指针juanchopanza说。

Or you can use a function pointer as juanchopanza says.

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