c++ - 获取临时地址 [-fpermissive]

Question

我知道这个问题已经回答了。但我只是想确认一下我的理解。

这是我的代码片段。来自this .

#include <iostream>
using namespace std;

class Base
{
    void a() { cout << "a  "; }
    void c() { cout << "c  "; }
    void e() { cout << "e  "; }

    // 2. Steps requiring peculiar implementations are "placeholders" in base class
    virtual void ph1() = 0;
    virtual void ph2() = 0;

  public:

    // 1. Standardize the skeleton of an algorithm in a base class "template method"
    virtual ~Base() = default;
    void execute()
    {
        a();
        ph1();
        c();
        ph2();
        e();
    }
};

class One: public Base
{
    // 3. Derived classes implement placeholder methods
    /*virtual*/ void ph1() { cout << "b  "; }
    /*virtual*/ void ph2() { cout << "d  "; }
};

class Two: public Base
{
    /*virtual*/ void ph1() { cout << "2  "; }
    /*virtual*/ void ph2() { cout << "4  "; }
};

int main()
{
  Base *array[] =
  {
      &One(), &Two()
  };
  for (int i = 0; i < 2; i++)
  {
      array[i]->execute();
      cout << '\n';
  }
}

当我编译时，它给出了错误作为标题:

error: taking address of temporary [-fpermissive]
&One(), &Two()
error: taking address of temporary [-fpermissive]
&One(), &Two()

所以，我尝试在互联网上查找。正如他们所说:

&A() is creating a temporary object which gets destructed on exit of the full expression automagically...

当我更改错误行

&One(), &Two()

到

new One(), new Two()

然后，它起作用了。

但是，我如何使原始代码像作者写的那样工作？我应该使用 delete 吗

delete array[i];

Answer 1

借助现代 C++ 功能(11 及更高版本)，您可以使用 std::vector<std::unique_ptr<Base>> 处理此类多态数组. vector允许自动销毁和扩展，以及unique_ptr将在其自身销毁时销毁对象:

std::vector<std::unique_ptr<Base>> array;
array.emplace_back(new One());
array.emplace_back(new Two());
for(auto &p : array)
    p->execute();
// no explicit cleanup is required here

您可以选择其他智能指针类作为 vector 的元素，甚至可以使用std::array。作为固定大小的容器，但所有方法的总体思路都是相同的:

Try not to handle memory management manually, use STL primitives for such low-level actions.