有关remove&erase

问题出在STL中多remove算法上面，这货根本就没有把合适的元素删除！！NEVER！它做的事情类似于排序，把需要删除的位置的元素用其他对象替换掉，而且调用多就是operator=。

看代码：

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

namespace{
  class MyObject{
    public:
      // Constructor
      MyObject(int data):
        m_data(data)
      {
        cout<< "Constructing!:" << data <<endl;
      }

      // Copy constructor
      MyObject( const MyObject &obj ):
        m_data(obj.m_data)
      {
        cout<< "Copying: " << m_data << endl;
      }

      // Assign operator
      const MyObject& operator=(const MyObject& obj)
      {
        m_data = obj.m_data;
        cout<< "Assigning: " << m_data << endl;
        return *this;
      }

      // Compare opertor
      bool operator==(const MyObject &obj)
      {
        if( m_data == obj.m_data )
          return true;
        else
          return false;
      }

      // Destructor
      ~MyObject()
      {
        cout<< "Destructing: " << m_data << endl;
      }
  
    int m_data;
  };
}

void removeEarseTestMain()
{
  vector<MyObject> vec;

  vec.push_back(MyObject(1));
  vec.push_back(MyObject(2));
  vec.push_back(MyObject(3));
  vec.push_back(MyObject(2));
  vec.push_back(MyObject(4));
  vec.push_back(MyObject(5));


  cout<< "prepare finished! ===========================================" << endl;

  auto iter = remove(vec.begin(), vec.end(), 2); 

  cout<< "remove finished! ===========================================" << endl;
  
  vec.erase(iter, vec.end());
  
  cout<< "erase finished! ===========================================" << endl;

}

结果：

Constructing!:1
Copying: 1
Destructing: 1
Constructing!:2
Copying: 2
Copying: 1
Destructing: 1
Destructing: 2
Constructing!:3
Copying: 3
Copying: 1
Copying: 2
Destructing: 1
Destructing: 2
Destructing: 3
Constructing!:2
Copying: 2
Destructing: 2
Constructing!:4
Copying: 4
Copying: 1
Copying: 2
Copying: 3
Copying: 2
Destructing: 1
Destructing: 2
Destructing: 3
Destructing: 2
Destructing: 4
Constructing!:5
Copying: 5
Destructing: 5
prepare finished! ===========================================
Constructing!:2
Destructing: 2
Constructing!:2
Destructing: 2
Constructing!:2
Destructing: 2
Assigning: 3
Constructing!:2
Destructing: 2
Constructing!:2
Destructing: 2
Assigning: 4
Constructing!:2
Destructing: 2
Assigning: 5
remove finished! ===========================================
Destructing: 4
Destructing: 5
erase finished! ===========================================
Destructing: 1
Destructing: 3
Destructing: 4
Destructing: 5

 

注意：中间的很多“Destructing: 2”估计是析构临时对象，请忽略！

由此可见erase才是真正释放空间的操作。

由这个代码的输出可以看出来，C++0x中的右值引用以及move语义编程是多么重要啊，如果加上这个特性，开始位置就不会出现临时对象多频繁构造和析构了！