百思不得其解的问题
#include <iostream>
#include <list>
using namespace std;

class CAnimal
{
public:
CAnimal(){};
virtual ~CAnimal(){};
virtual void Sound()
{
cout<<"animal sound\n";
}

};

class CDog : public CAnimal
{
public:
CDog(){};
~CDog(){};
virtual void Sound()
{
cout<<"dog sound\n";
}
};

class CCat : public CAnimal
{
public:
CCat(){};
~CCat(){};
virtual void Sound()
{
cout<<"cat sound\n";
}
};

int main()
{
list<CAnimal*> animalList;
CAnimal a1;
CAnimal a2;
CAnimal a3;
CDog d1;
CDog d2;
CDog d3;
CCat c1;
CCat c2;
CCat c3;
CCat c4;
animalList.push_back( &d1 );
animalList.push_back( &a2 );
animalList.push_back( &d3 );
animalList.push_back( &c3 );
animalList.push_back( &c4 );
animalList.push_back( &d2 );
animalList.push_back( &c1 );
animalList.push_back( &a3 );
animalList.push_back( &c2 );
animalList.push_back( &a1 );
for ( list<CAnimal*>::iterator it = animalList.begin(); it != animalList.end(); ++it )
{
it->Sound();
}
}

1>d:\working\test\test\test.cpp(36) : error C2839: 重载的“operator ->”的无效返回类型“CAnimal **”
1>d:\working\test\test\test.cpp(36) : error C2039: “CAnimal”: 不是“std::list<_Ty>::_Iterator<_Secure_validation>”的成员

[解决办法]
简单地说，因为模板本身使用类型作为参数，所以它不接受隐式类型转换
派生类指针可以隐式转换为基类指针，但模板不吃这一套
[解决办法]
按贴出的代码，36行哪来的->和std::list？
it本身是个迭代器，相当于一个指针，指向CAnimal*。(*it)->Sound()看看