c++ - multimap 清除

Question

这是我使用多 map 制作的一个简单的事件系统；当我使用 CEvents::Add(..) 方法时，它应该插入并进入多重映射。问题是，当我触发这些事件时， multimap 似乎是空的。我确定我没有调用删除方法 [CEvents::Remove]。这是代码:

//Code:
..
CEvents Ev;
Ev.Add("onButtonBReleased",OutputFST);
..

// "CEvents.h"
class CEvents
{
public:

    void            Add                     ( string EventName, void(*fn)(void));   
    void            Remove                  ( string EventName, void(*fn)(void));
    void            Trigger                 ( string EventName );

//protected:

    bool            Found;

    std::multimap<string,void(*)(void)> EventsMap;
    std::multimap<string,void(*)(void)>::iterator EvMapIt;
};



//CEvents.cpp
void CEvents::Add (string EventName, void (*fn)(void))
{
if (!EventsMap.empty())
{
    Found = false;

    for (EvMapIt = EventsMap.begin(); EvMapIt != EventsMap.end(); EvMapIt++)
    {
        if ((EvMapIt->first == EventName) && (EvMapIt->second == fn))
        {
        CTools tools;
        tools.ErrorOut("Function already bound to same event... Not registering event");
                Found = true;
            } 
        }

        if (!Found)
        {
            EventsMap.insert(std::pair<string,void(*)(void)>(EventName,fn));
            std::cout<<"Added, with size "<<(int) EventsMap.size()<<std::endl; //Getting 1
        }
}
else
{
    EventsMap.insert (std::pair<string,void(*)(void)>(EventName,fn));
    std::cout<<"Added, with size "<<(int) EventsMap.size()<<std::endl; //Getting 1
}
}

void CEvents::Trigger (string EventName)
{
std::cout<<"Triggering init"<<std::endl;
std::cout<<(int) EventsMap.size()<<std::endl; //Getting 0

for (EvMapIt = EventsMap.begin(); EvMapIt != EventsMap.end(); EvMapIt++)
    {
        std::cout<<"Triggering proc"<<std::endl;
        if (EvMapIt->first == EventName)
    EvMapIt->second();
}
}

Answer 1

它不应该是一个代码审查网站，但我无法自拔......

// "CEvents.h"
class CEvents
{
public:
    typedef void (*Callback)(void);

    // 1. Don't use `using namespace` in header files
    // 2. Pass by const reference to avoid a copy
    // 3. Function Pointers are easier to deal with when typedef'd
    void Add(std::string const& EventName, Callback fn);
    void Remove(std::string const& EventName, Callback fn);
    void Trigger(std::string const& EventName);

// Attributes should be `private` or `public`, `protected` is for functions.
// If you read otherwise, consider how this violates encapsulation.
//protected:

private: // cause nobody's touching my stuff lest they break it!

    // useless in this class, should be local variables in the routines
    // bool Found;
    // MapType::iterator EvMapIt;

    // typedef make life easier, spelling that out each time is just tiring.
    typedef std::multimap<std::string, Callback> MapType;
    MapType EventsMap;
};

好吧，让我们去找源文件吧。

//CEvents.cpp

// Whole rewrite to use idiomatic interfaces
void CEvents::Add(std::string const& EventName, Callback fn)
{
    // Retrieve the range of callbacks registered for "EventName"
    std::pair<MapType::iterator, MapType::iterator> const range =
        EventsMap.equal_range(EventName);

    // Check that this callback is not already registered.
    for (MapType::iterator it = range.first, end = range.second;
         it != end; ++it)
    {
        if (it->second == fn) {
            // Are you sure `ErrorOut` should not be a free function
            // or at least a `static` function ?
            // It feels weird instantiating this class.
            CTools tools;
            tools.ErrorOut("Function already bound to same event..."
                           " Not registering event");
            // If it is in there, nothing to do, so let's stop.
            return;
        }
    }

    // If we are here, then we need to add it.
    // Let's give a hint for insertion, while we are at it.
    EventsMap.insert(range.second, std::make_pair(EventName, fn));

    // the (int) cast was C-like (bah...) and unnecessary anyway
    std::cout << "Added, with size " << EventsMap.size() << std::endl; 
}


void CEvents::Trigger (std::string const& EventName)
{
    std::cout << "Triggering init" << std::endl;
    std::cout <<  EventsMap.size() << std::endl; //Getting 0

    // Retrieve the range of callbacks registered for `EventName`
    std::pair<MapType::const_iterator, MapType::const_terator> const range =
        EventsMap.equal_range(EventName);

    // Call each callback in turn
    for (MapType::const_iterator it = range.first, end = range.second;
         it != end; ++it)
    {
        it->second();
    }
}

当然，它可能无法解决您的问题，但它比应该有助于缩小问题范围的时间短得多。

当然，使用 std::set<std::pair<std::string, Callback>> 可能更简单因为它会确保 (EventName, fn) 的唯一性自动配对...尽管分派(dispatch)事件的代码会稍微复杂一些，所以不确定它是否会成功(代码方面或性能方面)。