求助抽象类指针未初始化

[呆萌霍比特人的傻大脚板]

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


class Shape {
 public:
  Shape() {}
  virtual ~Shape() {}
  virtual double GetArea() = 0;  
  virtual double GetPerim() = 0;
  virtual void Draw() = 0;
};

class Circle : public Shape {
 public:
  Circle(int radius) : itsRadius(radius) {}
  virtual ~Circle() {}  
  double GetArea() {
    return 3.14 * itsRadius * itsRadius;
  } 
  double GetPerim() { return 2 * 3.14 * itsRadius; }
  void Draw();

 private:
  int itsRadius;
};

void Circle::Draw() { cout << "Circle drawing routing here!\n"; }

class Rectangle : public Shape {
 public:
  Rectangle(int len, int width) : itsLength(len), itsWidth(width) {}
  virtual ~Rectangle() {}
  double GetArea() { return itsLength * itsWidth; }
  double GetPerim() { return 2 * itsLength * itsWidth; }
  virtual int GetLength() { return itsLength; }
  virtual int GetWidth() { return itsWidth; }
  void Draw();

 private:
  int itsWidth;
  int itsLength;
};

void Rectangle::Draw() {
  for (int i = 0; i < itsLength; i++) {
    for (int j = 0; j < itsWidth; j++) cout << "x ";
    cout << "\n";
  }
}

class Square : public Rectangle {
 public:
  Square(int len);
  Square(int len, int width);
  virtual ~Square(){};
  double GetPerim() { return 4 * GetLength(); }
  double GetArea() { return GetLength() * GetLength(); }
};

Square::Square(int len) : Rectangle(len, len) {}
Square::Square(int len, int width) : Rectangle(len, width) {
  if (GetLength() != GetWidth()) cout << "error not a Square!\n";
}

int main() {
  int choice;
  Shape *sp;
  bool fQuit = false;
  while (fQuit == false) {
    cout << "(1)Circle (2)Rectangle (3)Square (0)Quit:";
    cin >> choice;
    switch (choice) {
      case 1:
        sp = new Circle(5);

        break;
      case 2:
        sp = new Rectangle(4, 6);

        break;
      case 3:
        sp = new Square(5);

        break;
      case 0:
        fQuit = true;
        break;
    }
     if (fQuit==false) {
       sp->Draw();//编译时这行出错,应该是sp没有在switch中建立派生类对象,导致仍是抽象类指针.但我从流程上看并没有错的地方.求高手帮忙解惑.
       delete sp;
       cout << endl;
     }
  }
  return 0;
}

[SleekStone]

因为现在的编译器都比较智能了，会检查到第69行的sp没有被初始化，将第69行代码改为Shape *sp = nullptr;就能编过了，然后你这个代码有点问题，你可以试着输入5，修改的话：将第69行代码改为Shape *sp = nullptr；第91行改为 if (nullptr != sp)

[呆萌霍比特人的傻大脚板]

引用 1 楼 SleekStone 的回复:

因为现在的编译器都比较智能了，会检查到第69行的sp没有被初始化，将第69行代码改为Shape *sp = nullptr;就能编过了，然后你这个代码有点问题，你可以试着输入5，修改的话：将第69行代码改为Shape *sp = nullptr；第91行改为 if (nullptr != sp)

switch里面没有写default,我现在补了上去谢谢. 主要是我按视频教程打的,他在VS 2010上能过,我这里过不了,就觉得很郁闷.我也猜应该是编译器的关系,但就是不知道如何改,我曾试着把91行改成if(sp!=NULL)也不行...,原来要手动指明是nullptr.谢谢...