Question

我打算编写一个使用虚函数进行多边形计算的程序，但是在完成程序后，会出现BLOCK_TYPE_IS_VALID（pHead - ＆gt; nBlockUse）错误

// pointers to base class
#include <iostream>
#include "Polygon.h"
#include "Rectangle.h"
#include "Triangle.h"

using namespace std;

int main() {
Rectangle rect1(4, 5);
Rectangle rect2(3, 3);
Triangle tri(4, 4, false);
int triLength[3] = { 5, 4, 3 };
tri.setsideLength(triLength);

Polygon * p = &rect1;
cout << "Rectangle 1: " << endl;
cout << "\tArea: " << p->area() << endl;
cout << "\tSide: ";
p->printsideLength();
rect1.printsideLength();
cout << "\tTotal Side Length: " << p->totalsideLength() << endl;
p = &rect2;
cout << "Rectangle 2: " << endl;
cout << "\tArea: " << p->area() << endl;
cout << "\tSide: ";
p->printsideLength(); 
rect2.printsideLength();
cout << "\tTotal Side Length: " << p->totalsideLength() << endl;
p = &tri;
cout << "Triangle: " << endl;
cout << "\tArea: " << p->area() << endl;
cout << "\tSide: ";
p->printsideLength(); 
cout << "\tTotal Side Length: " << p->totalsideLength() << endl;
system("pause");
return 0;
}

这是程序的main.cpp，程序无需输入任何只需要显示结果的东西。

以下是三类（cpp＆amp; h）

#ifndef Polygon_H
#define Polygon_H

#include <iostream>
using namespace std;

class Polygon{
private:
int noOfSide;
bool isAllSideEqual;
int* sideLength;
public:
Polygon();
Polygon(int n,bool s);
~Polygon();
void setsideLength(int* sl);
void printsideLength();
int totalsideLength();
virtual int area();
};

#endif

#include "Polygon.h"
#include <iostream>
using namespace std;

Polygon::Polygon(){
    noOfSide = 3;
    isAllSideEqual = false;
    sideLength = new int[noOfSide];
    sideLength = &sideLength[noOfSide];
};


Polygon::Polygon(int n,bool s){
    if (n<3)
    {
        noOfSide = 3;
        isAllSideEqual = false;}
    else
    {
        noOfSide = n;
        isAllSideEqual = s;
    };
    sideLength = new int[noOfSide];
    sideLength = &sideLength[noOfSide];

};

Polygon::~Polygon(){
    delete[] sideLength;
};


void Polygon::setsideLength(int* sl){
    for(int i=0;i<noOfSide;i++)
        sideLength[i] = sl[i];
};
void Polygon::printsideLength(){
    for(int i=0;i<noOfSide;i++)
        cout << sideLength[i] <<" ";
};

int Polygon::totalsideLength(){
    int total = 0;
    for(int i=0;i<noOfSide;i++)
        total += sideLength[i];
    return total;
};
int Polygon::area(){
    return 0;
};

   #ifndef Triangle_H
   #define Triangle_H

  #include <iostream>
  #include "Polygon.h"
  using namespace std;

class Triangle:public Polygon
{
private:
    int width;
    int height;
public:
    Triangle(int w,int h,bool s);
    virtual int area();
};
#endif


 #include "Triangle.h"
 #include <iostream>
  using namespace std;
 Triangle::Triangle(int w,int h,bool s){
    width = w;
    height = h;
    Polygon(3,s);
};

int Triangle::area(){
    int total = 0;
    total = (width*height)/2;
    return total;
};


  #ifndef Rectangle_H
  #define Rectangle_H

  #include <iostream>
  #include "Polygon.h"
  using namespace std;

  class Rectangle:public Polygon{
  private:
  int width;
  int height;
 public:
  Rectangle(int w,int h);
  void printsideLength();
  virtual int area();
 };
 #endif

#include "Rectangle.h"
#include <iostream>
using namespace std;

Rectangle::Rectangle(int w,int h){
    width=w;
    height=h;
    if(width = height)
        Polygon(4,true);
    else
        Polygon(4,false);
    int* size =new int[4];
    size[0] = width;
    size[1] = height;
    size[2] = width;
    size[3] = height;
    Polygon::setsideLength(size);
};

void Rectangle::printsideLength(){
    for(int i=0;i<2;i++)
        cout<< width<<" "<<height <<" ";
};

int Rectangle::area(){
    int total =0;
    total = width*height;
    return total;
};

程序没有任何编译错误，因此唯一的问题是关于内存但哪里错了？虚函数部分是错误还是其他任何部分？

Answer 1

有几个问题。

在Polygon构造函数中，

中的第二行

sideLength = new int[noOfSide];
sideLength = &sideLength[noOfSide];

是主要的错误它会使sideLength指向您刚刚分配的内存的末尾使用此指针是未定义的您之后复制到该位置并将其传递给delete，这两个都无效您只需要sideLength = new int[noOfSide]; 您还需要一个正确的复制构造函数和赋值运算符，因为该类是手动管理内存。

（你真正应该做的是使用std::vector<int>并停止担心内存分配。）

在您的子类构造函数中，Polygon(3,s);等不会初始化您的基类，它们会创建一个未命名的Polygon，并立即将其丢弃。

您应该初始化初始化列表中的基类（以及其他成员）：

Triangle::Triangle(int w, int h, bool s)
  : Polygon(3, s),
    width(w),
    height(h)
{
}

Rectangle的构造函数存在同样的问题，并且使用了=，您应该使用相等的==添加问题。Rectangle::Rectangle(int w, int h) : Polygon(4, w == h), width(w), height(h) { int size[] = {width, height, width, height}; setsideLength(size); }。（如果启用警告，您的编译器可以向您发出警告。这样做，并听取它们的意见。）

public class MyClass<T extends MyInterface> {

   private T myGeneric;
   private String desc;

   ....
}

public interface MyInterface {
   String getSomeString();
}

public class MySubClass implements MyInterface {
  private String info;
  ....

  @Override
  public getSomeString() {
     return "";
  }
}

BLOCK_TYPE_IS_VALID（pHead - ＆gt; nBlockUse）错误

1 个答案: