如何使用C++STL排序对具有继承性的对象数组进行排序

How I can use C++ STL Sort for sorting array of object with inheritance

本文关键字：排序 对象 数组 继承性 何使用 C++STL      更新时间：2023-10-16

我试图使用c++STL sort()按对象的一个属性对对象数组进行排序，但总是收到一个错误：

main.cpp: In function 'bool sortByArea(const Shape*, const Shape*)':
main.cpp:54:22: error: passing 'const Shape' as 'this' argument of 'double Shape::getArea()' discards qualifiers [-fpermissive]
  return lhs->getArea() < rhs->getArea();
                      ^
main.cpp:54:39: error: passing 'const Shape' as 'this' argument of 'double Shape::getArea()' discards qualifiers [-fpermissive]
  return lhs->getArea() < rhs->getArea();

这是我的代码：

形状.cpp

#include "Shape.h"
Shape::Shape(){
    width=0;
    height=0;
    area=0;
    perimeter=0;
}
Shape::Shape(double newwidth, double newheight, double newarea, double newperimeter){
    width=newwidth;
    height=newheight;
    area=newarea;
    perimeter=newperimeter;
}
Shape::~Shape(){
}
double Shape::getWidth(){
    return width;
}
double Shape::getHeight(){
    return height;
}
double Shape::getArea(){
    return area;
}
double Shape::getPerimeter(){
    return perimeter;
}
double Shape::calArea(){
    return 0;
}
double Shape::calPerimeter(){
    return 0;
}

Circle.cpp

#include "Circle.h"
#include <cmath>
#define PI 3.141592654
Circle::Circle(){
    width = height = 0;
    area=0; perimeter=0;
}
Circle::Circle(double newradius){
    width = height = newradius;
    area = calArea(); perimeter = calPerimeter();
}
Circle::~Circle(){
}
double Circle::calArea(){
    return (pow(width,2)*PI);
}
double Circle::calPerimeter(){
    return (width * PI * 2);
}

main.cpp

#include "Shape.h"
#include "Circle.h"
#include "Rectangle.h"
#include "Square.h"
#include <fstream>
#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;
const int size = 200;
int cshape = 0; int rshape = 0; int sshape = 0;
void input_circle(Shape* mshape){
    ifstream file;
    int i;
    double r;
    file.open("circle.txt");
    while (file >> r){
        Circle crl(r);
        mshape[cshape]=crl;
        cshape++;
    }
    file.close();
}
bool sortByArea(const Shape * lhs, const Shape * rhs) { 
    return lhs->getArea() < rhs->getArea(); 
}

int main(){
    Shape* shapecir;
    shapecir = new (nothrow) Circle[size]();
    input_circle(shapecir);
    int i;
    cout << "Circle" << endl;
    sort(shapecir,shapecir+size,sortByArea);
    for (i=0;i<cshape;i++)
        cout << shapecir[i].getArea() << " " << shapecir[i].getPerimeter() << endl;
    return 0;
}

我试着在网上找些东西，但找不到任何有用的东西。

您应该在编写这些函数时对它们进行了测试。问题就在这里：

double Shape::getArea(){
    return area;
}
bool sortByArea(const Shape * lhs, const Shape * rhs) { 
    return lhs->getArea() < rhs->getArea(); 
}

您正确地给出了sortByArea常量指针参数，但忽略了使getArea成为常量函数。编译器告诉您，在您禁止更改形状之后，您正在命令代码执行可能更改形状的操作。

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