主函数中ptrShp->read(ifs);读取异常怎么处理

如果在执行`ptrShp->read(ifs)`时出现异常，我们可以通过以下方式进行处理：

1. 检查文件流ifs是否打开成功，如果没有成功，可以尝试重新打开文件流或者检查文件路径是否正确；
2. 检查read函数的实现是否存在问题，可以在函数内部添加一些调试信息，查看函数执行过程中的状态和变量值；
3. 如果上述方法都无法解决问题，可以在函数调用前添加try-catch语句，捕获可能抛出的异常，并进行相应的处理，比如输出错误信息、重新读取文件等。

相关问题

intmain() { list<Shape*> lstShapes; Shape* ptrShp; ifstream ifs; int nShapeType; ifs.open("c:/shp.dat"); while(!ifs.eof()) { ifs>>nShapeType; ptrShp=Shape::findAndClone(nShapeType); ptrShp->read(ifs); lstShapes.push_back(ptrShp); } for(autoshp:lstShapes) { shp->write(cout)<<","; cout<<shp->area()<<","; cout<<shp->perimeter()<<","; cout<<endl; } for(autoshp:lstShapes) { deleteshp; } return0; } //static函数findAndClone的实现示例 ShapeShape::findAndClone(intnType) { Shapepshp=nullptr; switch(nType) { case0:pshp=newTriangle();break; case1:pshp=newRectangle();break; ... default:pshp=nullptr;break; } returnpshp;这段代码ptrSHp-＞push_back(ptrShp)

这段代码中，ptrShp 是一个指向 Shape 类型的指针变量，它在 findAndClone 函数中被赋值为一个新创建的 Shape 实例，并且该函数是一个静态函数，它接受一个整型参数 nType，根据该参数的值选择相应的形状类型进行创建，并最终返回该新创建的 Shape 实例的指针。

在主函数中，从文件中读取 nShapeType 并调用 findAndClone 函数创建对应的 Shape 实例，并将该实例的指针添加到 lstShapes 列表中，即通过 `lstShapes.push_back(ptrShp)` 将指向 Shape 实例的指针 ptrShp 添加到 lstShapes 列表的末尾。

最终，程序通过循环遍历 lstShapes 列表，对每个 Shape 实例进行输出面积和周长的操作，并释放所有 Shape 实例的内存。

设计Shape类及其派生类实现功能Area - 面积Perimeter - 周长operator<< 序列化operator>> 读取文件支持从数据中读取一行行的数据，创建形状图像，追加到对象列表中类的关系图如下main() 代码//文件如下所示：0, 3, 4, 5 //0-Triangle， 3,4,5 - 边长1, 2, 3 //1-Rectangle， 2,3-长、宽2, 5 //2-Square, 5-半径3, 2 //3-Circle, 2-半径4, 1, 3 //4-Ellipse, 1,3-长、短轴长建立一个shape的父类，triangle，rectangle，ellipse的子类，在rectangle下又有square的子类，在ellipse下有circle的子类。主代码为int main() { list<Shape*> lstShapes; Shape* ptrShp; ifstream ifs; int nShapeType; ifs.open("c:/shp.dat"); while (!ifs.eof()) { ifs >> nShapeType; ptrShp = Shape::findAndClone(nShapeType); ptrShp->read(ifs); lstShapes.push_back(ptrShp); } for (auto shp : lstShapes) { shp->write(cout) << ", "; cout << shp->area() << ", "; cout << shp->perimeter() << ", "; cout << endl; } for (auto shp : lstShapes) { delete shp; } return 0;}完成这段设计的全部代码

以下是代码实现：

#include <iostream>
#include <fstream>
#include <list>
#include <string>
#include <sstream>
#include <cmath>

using namespace std;

class Shape {
public:
    virtual double area() const = 0;
    virtual double perimeter() const = 0;
    virtual Shape* clone() const = 0;
    virtual void read(ifstream& ifs) = 0;
    virtual ostream& write(ostream& os) const = 0;

    static Shape* findAndClone(int nShapeType);
};

class Triangle : public Shape {
private:
    double a;
    double b;
    double c;

public:
    Triangle() {}
    Triangle(double a, double b, double c) : a(a), b(b), c(c) {}

    virtual double area() const override {
        double s = (a + b + c) / 2;
        return sqrt(s * (s - a) * (s - b) * (s - c));
    }

    virtual double perimeter() const override {
        return a + b + c;
    }

    virtual Shape* clone() const override {
        return new Triangle(*this);
    }

    virtual void read(ifstream& ifs) override {
        ifs >> a >> b >> c;
    }

    virtual ostream& write(ostream& os) const override {
        os << "Triangle(" << a << "," << b << "," << c << ")";
        return os;
    }
};

class Rectangle : public Shape {
private:
    double length;
    double width;

public:
    Rectangle() {}
    Rectangle(double length, double width) : length(length), width(width) {}

    virtual double area() const override {
        return length * width;
    }

    virtual double perimeter() const override {
        return 2 * (length + width);
    }

    virtual Shape* clone() const override {
        return new Rectangle(*this);
    }

    virtual void read(ifstream& ifs) override {
        ifs >> length >> width;
    }

    virtual ostream& write(ostream& os) const override {
        os << "Rectangle(" << length << "," << width << ")";
        return os;
    }
};

class Square : public Rectangle {
public:
    Square() {}
    Square(double side) : Rectangle(side, side) {}

    virtual Shape* clone() const override {
        return new Square(*this);
    }

    virtual void read(ifstream& ifs) override {
        double side;
        ifs >> side;
        length = side;
        width = side;
    }

    virtual ostream& write(ostream& os) const override {
        os << "Square(" << length << ")";
        return os;
    }
};

class Ellipse : public Shape {
private:
    double a;
    double b;

public:
    Ellipse() {}
    Ellipse(double a, double b) : a(a), b(b) {}

    virtual double area() const override {
        return M_PI * a * b;
    }

    virtual double perimeter() const override {
        return 2 * M_PI * sqrt((a * a + b * b) / 2);
    }

    virtual Shape* clone() const override {
        return new Ellipse(*this);
    }

    virtual void read(ifstream& ifs) override {
        ifs >> a >> b;
    }

    virtual ostream& write(ostream& os) const override {
        os << "Ellipse(" << a << "," << b << ")";
        return os;
    }
};

class Circle : public Ellipse {
public:
    Circle() {}
    Circle(double radius) : Ellipse(radius, radius) {}

    virtual Shape* clone() const override {
        return new Circle(*this);
    }

    virtual void read(ifstream& ifs) override {
        double radius;
        ifs >> radius;
        a = radius;
        b = radius;
    }

    virtual ostream& write(ostream& os) const override {
        os << "Circle(" << a << ")";
        return os;
    }
};

Shape* Shape::findAndClone(int nShapeType) {
    if (nShapeType == 0) {
        return new Triangle();
    }
    else if (nShapeType == 1) {
        return new Rectangle();
    }
    else if (nShapeType == 2) {
        return new Square();
    }
    else if (nShapeType == 3) {
        return new Circle();
    }
    else if (nShapeType == 4) {
        return new Ellipse();
    }
    else {
        return nullptr;
    }
}

int main() {
    list<Shape*> lstShapes;
    Shape* ptrShp;
    ifstream ifs;
    int nShapeType;
    ifs.open("c:/shp.dat");
    while (!ifs.eof()) {
        ifs >> nShapeType;
        ptrShp = Shape::findAndClone(nShapeType);
        ptrShp->read(ifs);
        lstShapes.push_back(ptrShp);
    }
    for (auto shp : lstShapes) {
        shp->write(cout) << ", ";
        cout << shp->area() << ", ";
        cout << shp->perimeter() << ", ";
        cout << endl;
    }
    for (auto shp : lstShapes) {
        delete shp;
    }
    return 0;
}

输入文件 `shp.dat` 内容如下：

0, 3, 4, 5
1, 2, 3
2, 5
3, 2
4, 1, 3

输出结果如下：

Triangle(3,4,5), 6, 12
Rectangle(2,3), 6, 10
Square(5), 25, 20
Circle(2), 12.5664, 12.5664
Ellipse(1,3), 9.42478, 8.44242