如何在带有输入的地图元素方法上使用std :: for_each? [英] How to use std::for_each on a map element method with input?

问题描述

我有:

struct Mystruct
{
    void Update(float Delta);
}

typedef std::map<int, Mystruct*> TheMap;
typedef TheMap::iterator         TheMapIt;

TheMap Container;

并想这样做:

for(TheMapIt It = Container.begin(), Ite = Container.end(); It != Ite; ++It)
{
    It->second->Update(Delta);
}

使用std::for_each，该怎么做?

我想我可以声明如下函数:

I think I can declare function like:

void Do(const std::pair<int, Mystruct*> Elem)
{
    Elem->Update(/*problem!*/); ---> How to pass Delta in?
}

或制作另一个结构:

struct Doer
{
    Doer(float Delta): d(Delta) {}

    void operator(std::pair<int, Mystruct*> Elem)
    {
        Elem->Update(d);
    }
}

但这需要一个新的结构.

But this requires a new struct.

我要实现的是使用普通的std::for_each以及std::bind_1st，std::mem_fun之类的东西，就像std::vector一样，

What I wants to achieve is using plain std::for_each with something like std::bind_1st, std::mem_fun like the way with std::vector, is it possible?

请先考虑使用std的方式，然后再使用boost，谢谢！

Please consider using std way before using boost, thanks!

我已经引用了这个，但是它并没有提及带有输入的成员函数... 我将如何使用for_each删除STL映射中的每个值?

I've referenced this but it doesnt metion about member function with input... How would I use for_each to delete every value in an STL map?

推荐答案

这只是编码风格之间的一种折衷，for循环和for_each没有什么大的区别，下面是for循环以外的另外两种方法:

This is just a trade between coding style, for loop and for_each doesn't make big difference, below are two other approaches besides for loop:

如果您使用C ++ 11，则可以尝试使用lambda:

If you use C++11, could try lambda:

std::for_each(TheMap.begin(), TheMap.end(), 
              [](std::pair<int, Mystruct*>& n){ n.second->Update(1.0); });

或者在C ++ 03中，您可以向包装类添加一个成员函数，然后调用std::bind1st和std::mem_fun

Or in C++03, you could add a member function to wrapper class then call std::bind1st and std::mem_fun

struct MapWrapper
{
  MapWrapper(int value=1.0):new_value(value) {}

  void Update(std::pair<int, Mystruct*> map_pair)
  {
    map_pair.second->Update(new_value);
  }
  void setValue(float value) { new_value = value; }
  float new_value;
  std::map<int, Mystruct*> TheMap;
};

MapWrapper wrapper;
wrapper.setvalue(2.0);
std::for_each(wrapper.TheMap.begin(), 
              wrapper.TheMap.end(),std::bind1st(std::mem_fun(&MapWrapper::Update), &wrapper));

写一个函子不是一个坏选择，为什么反对呢?函子可提供更好的设计，因为它提供了清晰明了的目的.

Write a functor isn't a bad choice, why you are against it? A functor provides better design as it provides clean and clear purpose.

struct Doer
{
    Doer(float Delta): d(Delta) {}

    void operator()(std::pair<int, Mystruct*> e)
    {
      e.second->Update(d);
    }
    float d;
};
Doer doer(1.0);
std::for_each(wrapper.TheMap.begin(), wrapper.TheMap.end(), doer);

这篇关于如何在带有输入的地图元素方法上使用std :: for_each?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！