如何使用自定义 .begin() 和 .end() 循环 std::set？

Question

如果我有一套例如，内容如下：0,1,2,3,8,13,56,532,

我将如何处理从 3 到 532 到 0 到 3 的 for(auto it = xxxxx; y ? z; ++it)？

喜欢：

magic.start(3);
for(auto i: magic)
    std::cout << i << " ";

那会打印出来：

3 8 13 56 532 0 1 2

编辑：可能有人对最终结果感兴趣（感谢所有答案）：

bool SpectateNextPlayer(int playerid)
{
    if (PlayerCurrentlySpectating[playerid] == INVALID_PLAYER_ID)
        return false;

    auto current = PlayersOnline.find(PlayerCurrentlySpectating[playerid]);

    for (auto it = current; it != PlayersOnline.end(); ++it)
        if (PlayerSpactatable(*it) && (*it) != PlayerCurrentlySpectating[playerid])
            if (PlayerSpectateOtherPlayer(playerid, *it))//check here if playerid != *it
                return true;

    for (auto it = PlayersOnline.begin(); it != current; ++it)
        if (PlayerSpactatable(*it) && (*it) != PlayerCurrentlySpectating[playerid])
            if (PlayerSpectateOtherPlayer(playerid, *it))
                return true;

    return !DisablePlayerSpectate(playerid);
}

bool SpectatePreviousPlayer(int playerid)
{   
    if (PlayerCurrentlySpectating[playerid] == INVALID_PLAYER_ID)
        return false;

    auto rcurrent = find(PlayersOnline.rbegin(), PlayersOnline.rend(), PlayerCurrentlySpectating[playerid]);

    for (auto it = rcurrent; it != PlayersOnline.rend(); ++it)
        if (PlayerSpactatable(*it) && (*it) != PlayerCurrentlySpectating[playerid])
            if (PlayerSpectateOtherPlayer(playerid, *it))
                return true;

    for (auto it = PlayersOnline.rbegin(); it != rcurrent; ++it)
        if (PlayerSpactatable(*it) && (*it) != PlayerCurrentlySpectating[playerid])
            if (PlayerSpectateOtherPlayer(playerid, *it))
                return true;

    return !DisablePlayerSpectate(playerid);
}

Answer 1

你可以这样做（有两个循环）。

代码使用set::find() 来追踪您希望从哪个元素开始。然后它将从 find() 返回的迭代器中打印，直到集合结束。请注意，为简单起见，我没有检查 find() 返回的内容。

在第二个循环中，它将从头开始打印，直到遇到第一个循环开始的元素。

#include <iostream>
#include <set>

int main ()
{
  std::set<int> myset;
  myset.insert (0);
  myset.insert (1);
  myset.insert (2);
  myset.insert (3);
  myset.insert (8);
  myset.insert (13);
  myset.insert (56);
  myset.insert (532);

    std::cout << "myset contains:";
    std::set<int>::iterator it1;
    it1=myset.find(3);
    for (std::set<int>::iterator it = it1; it!=myset.end(); ++it)
      std::cout << ' ' << *it;
    std::cout << '\n';

    for (std::set<int>::iterator it2=myset.begin(); *it2!=*it1; ++it2)
      std::cout << ' ' << *it2;
    std::cout << '\n';


  return 0;
}

输出：

myset contains: 3 8 13 56 532
 0 1 2

---

为了向后执行此操作，您可以在this 回答中执行类似操作。

Answer 2

auto i = magic.find(3);
if (i != magic.end())
{
    auto finito = i;
    do
    {
        std::cout << *i << ' '; // or whatever you want to do with elements
        if (++i == magic.end()) i = magic.begin();
    } while (i != finito);
}

Answer 3

我猜你的意思是这样的：

bool first=true;
auto start = magic.find(3);
for(auto it=start;it!=start || first;it++){
   first = false;
   if(it == magic.end()){//make it like a circled list
     it = magic.begin();
   }
   if(it == magic.end()){
       cout << *it;
   } 
}