Question

test.exe中0x001AF3B5处的未处理异常：0xC0000005：访问冲突读取位置0x00000000。

在我的项目http://sourcemaking.com/design_patterns/command/cpp/2

中实现此代码时出现未处理的异常

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

class Command
{
// 1. Create a class that encapsulates an object and a member function
// a pointer to a member function (the attribute's name is "method")
Person *object; //    
void(Person:: *method)();
  public:
    Command(Person *obj = 0, void(Person:: *meth)() = 0)
{
    object = obj; // the argument's name is "meth"
    method = meth;
}
void execute()
{
    (object-> *method)(); // invoke the method on the object
}
};

class Person
{
string name;

// cmd is a "black box", it is a method invocation
// promoted to "full object status"
Command cmd; 
  public:
Person(string n, Command c): cmd(c)
{
    name = n;
}
void talk()
{
    // "this" is the sender, cmd has the receiver
    cout << name << " is talking" << endl;
    cmd.execute(); // ask the "black box" to callback the receiver
}
void passOn()
{
    cout << name << " is passing on" << endl;

    // 4. When the sender is ready to callback to the receiver,
    // it calls execute()
    cmd.execute(); 
}
void gossip()
{
    cout << name << " is gossiping" << endl;
    cmd.execute();
}
void listen()
{
    cout << name << " is listening" << endl;
}
};

int main()
{
  // Fred will "execute" Barney which will result in a call to passOn()
  // Barney will "execute" Betty which will result in a call to gossip()
  // Betty will "execute" Wilma which will result in a call to listen()
  Person wilma("Wilma", Command());
  // 2. Instantiate an object for each "callback"
  // 3. Pass each object to its future "sender"
  Person betty("Betty", Command(&wilma, &Person::listen));
  Person barney("Barney", Command(&betty, &Person::gossip));
  Person fred("Fred", Command(&barney, &Person::passOn));
  fred.talk();
}

根本不确定为什么？我实现了它，因为它没有变化，除了输出不同，只有2个人而不是4个。在命令的execute（）中尝试了一些调试和错误。

任何帮助或提示都会很棒！

编辑：实际上经过一些测试之后我改变了人们和正在发生的电话时不确定原因。

    Person player("Player", Command());
    Person master("House Master", Command(&player, &Person::passOn));
    master.talk();

Answer 1

问题是你允许空命令，你甚至可以不经检查就执行它。

将Command的构造函数更改为此应该可以解决问题：

Command(Person &obj, void(Person:: *meth)())

未处理的异常：访问冲突读取位置

1 个答案: