c++ - 无法使用 C++11 实例化抽象类

Question

为什么我不能在运行时像接口(interface)一样使用抽象类。

我得到输出:

1>c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(615): error C2259: 'Creature' : cannot instantiate abstract class
1>          due to following members:
1>          'std::string Creature::Move(std::vector<std::string,std::allocator<_Ty>> &)' : is abstract
1>          with
1>          [
1>              _Ty=std::string
1>          ]

1>          visual studio 2013\projects\cpp_demo\cpp_demo\creature.h(9) : see declaration of 'Creature::Move'
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(614) : while compiling class template member function 'void std::allocator<_Ty>::construct(_Ty *,const _Ty &)'
1>          with
1>          [
1>              _Ty=Creature
1>          ]

1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(752) : see reference to function template instantiation 'void std::allocator<_Ty>::construct(_Ty *,const _Ty &)' being compiled
1>          with
1>          [
1>              _Ty=Creature
1>          ]

1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\type_traits(580) : see reference to class template instantiation 'std::allocator<_Ty>' being compiled
1>          with
1>          [
1>              _Ty=Creature
1>          ]

1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector(650) : see reference to class template instantiation 'std::is_empty<_Alloc>' being compiled
1>          with
1>          [
1>              _Alloc=std::allocator<Creature>
1>          ]

1>          visual studio 2013\projects\cpp_demo\cpp_demo\main.cpp(7) : see reference to class template instantiation 'std::vector<Creature,std::allocator<_Ty>>' being compiled
1>          with
1>          [
1>              _Ty=Creature
1>          ]

我的代码:

int main()
{
    unique_ptr<vector<Creature>> pCreatures(new vector<Creature>);

    unique_ptr<Creature> pHuman(new Human());
    pCreatures->push_back(*pHuman);
}



#include "stdafx.h"
#include "Creature.h"

class Human : public Creature
{
public:
    virtual string Move(vector<string> &log);
};



#include "stdafx.h"
#include "IMove.h"

class Creature : public IMove
{
public:
    virtual string Move(vector<string> &log) = 0;
    virtual string GetState(vector<string> &log);
};

请帮忙。

Answer 1

您可以在 vector 或 unique_ptr 中使用抽象类，例如

#include <vector>
#include <memory>

using namespace std;

class Interface {
 public:
  virtual ~Interface() = 0;
};

Interface::~Interface() {}

class Implementation : public Interface {
};

int main(int argc, char** argv) {
  unique_ptr<Interface> p(new Implementation);
  vector<unique_ptr<Interface>> v;
  v.emplace_back(new Implementation);
  vector<Interface> vi;
  // This leads to compile error: vi.emplace_back();
}

此外，您可以使用 vector<Interface>只要你不调用任何可能调用 new Interface 的方法.例如，如果您只声明一个变量 vector<Interface> v;它编译，但如果你 push_back或 emplace_back或 resize , 然后它会出现编译错误，因为它们会调用 new Interface .

以上代码是在gcc-4.6.3下测试的。