Question

如果有人能够帮助我并告诉我它为什么存在段错误，我将非常感谢。谢谢！

注意：不允许以任何方式修改main函数。

#include <iostream>
#include <algorithm>
#include <functional>
#include <list>
#include <cmath>

class Object {
 public:
 private:
  float d;

 public:
  Object(float n) : d(n) {}
  Object() {}

  struct PointType {
    float x2;
    float y2;
    PointType(float x1, float y1) : x2(x1), y2(y1) {}
    PointType() {}
    float x() { return x2; }
    float y() { return y2; }
    PointType center() { return *this; }
    friend std::ostream &operator<<(std::ostream &os, const PointType &p) {
      os << p;

      return os;
    }
  };

  virtual void render() const {}
  virtual ~Object() {}
};

class Point : public Object {
 private:
  PointType mpoint;

 public:
  Point(const PointType &pt, float &y1) : Object(y1), mpoint(pt) {}
  Point(const PointType &pt) : mpoint(pt) {}
  Point() {}

  Point center() const { return *this; }
  float x() { return mpoint.x2; }
  float y() { return mpoint.y2; }
  friend std::ostream &operator<<(std::ostream &os, const Point &p) {
    os << p.center();
    return os;
  }
};

class VisiblePoint : public Point {
 public:
  VisiblePoint(const Object::PointType &point) : Point(point) {}

  void render() const override {
    std::cout << "Point at " << center() << std::endl;
  }
};

// A simple pseudo-random number generator.
class PseudoRandom {
  const int A = 101;
  const int B = 919;
  const int C = 10619863;

  int _current;

 public:
  PseudoRandom() : _current(0) {}

  int operator()() {
    _current = (A * _current + B) % C;
    _current += (_current < 0) ? C : 0;
    return _current;
  }

  int operator()(int n) { return (*this)() % n; }

  float operator()(float a, float b) {
    int result = (*this)();
    return a + (b - a) * static_cast<float>(result) / float(C);
  }
};

int main() {
  std::list<Object *> objects;
  PseudoRandom random;

  for (int i = 0; i < 10; ++i) {
    switch (random(1)) {
      case 0: {
        const Object::PointType point(random(0, 1), random(0, 1));
        objects.push_back(new VisiblePoint(point));
        break;
      }
      case 1: {
      }
      case 2: {
      }
      case 3: {
      }
      case 4: {
      }
    }
  }
  std::cout << "BEGIN" << std::endl;

  std::for_each(objects.begin(), objects.end(), std::mem_fn(&Object::render));

  std::cout << "END" << std::endl;

  for (const Object *object : objects) {
    delete object;
  }
  objects.clear();
}

Answer 1

由于以下原因，您的堆栈溢出

friend std::ostream& operator<<(std::ostream& os, const Point& p)
{
   os << p.center(); 
   return os;
}

调用自身而没有结束，因为Point::center()返回一个 Point （ center 仅返回该实例）

对于 PointType ，您有相同的堆栈溢出问题，可以将这些定义更改为例如：

friend std::ostream& operator<<(std::ostream& os, const Point& p)
{
    os << p.mpoint; 
    return os;
}

friend std::ostream& operator<<(std::ostream& os, const 
        PointType& p)
{   
    os << "x=" << p.x2 << ", y=" << p.y2;
    return os;              
}

编译和执行：

pi@raspberrypi:/tmp $ g++ -g -pedantic -Wextra -Wall c.cc
pi@raspberrypi:/tmp $ ./a.out
BEGIN
Point at x=0.00882667, y=0.89158
Point at x=0.015971, y=0.613159
Point at x=0.845152, y=0.360472
Point at x=0.186335, y=0.819929
Point at x=0.108734, y=0.982257
Point at x=0.0107827, y=0.0891412
Point at x=0.337889, y=0.126905
Point at x=0.567967, y=0.364747
Point at x=0.788968, y=0.685901
Point at x=0.889105, y=0.799651
END

请注意，成员 d 在 Object 中是私有的，如果我添加

，则无法访问它（也不能编写它）

friend std::ostream& operator<<(std::ostream& os, const Object & o) {
  os << "d=" << o.d;
  return os;
}

并将 Point 的operator<<修改为：

friend std::ostream& operator<<(std::ostream& os, const Point& p)
{
    os << p.mpoint << ", ";
    os << (const Object &) p;
    return os;
}

并在 Object 的默认构造函数中初始化 d ：

Object() : d(0) {}

编译和执行：

pi@raspberrypi:/tmp $ g++ -g -pedantic -Wextra -Wall c.cc
pi@raspberrypi:/tmp $ ./a.out
BEGIN
Point at x=0.00882667, y=0.89158, d=0
Point at x=0.015971, y=0.613159, d=0
Point at x=0.845152, y=0.360472, d=0
Point at x=0.186335, y=0.819929, d=0
Point at x=0.108734, y=0.982257, d=0
Point at x=0.0107827, y=0.0891412, d=0
Point at x=0.337889, y=0.126905, d=0
Point at x=0.567967, y=0.364747, d=0
Point at x=0.788968, y=0.685901, d=0
Point at x=0.889105, y=0.799651, d=0
END
pi@raspberrypi:/tmp $

C ++分段错误问题

1 个答案: