std :: set - 实现operator <？的正确方法？

Question

我已经与运营商<以下数据来实现：

enum eDataSetType 
{ 
    eData1, 
    eData2 
}; 

struct LocationData 
{ 
    bool operator < (const LocationData& other) const 
    { 
     if (mFileName < other.mFileName || 
      mDataSet < other.mDataSet || 
      mChunkId < other.mChunkId || 
      mAnimIndex < other.mAnimIndex) 
     { 
      return true; 
     } 
     return false; 
    } 

    eDataSetType mDataSet; 
    std::string mFileName; 
    Uint32 mChunkId; 
    Uint32 mAnimIndex; 
}; 

但使用std::set<LocationData>::insert我有时会收到以下消息时：

--------------------------- 
Microsoft Visual C++ Runtime Library 
--------------------------- 
Debug Assertion Failed! 

Program: C:\Windows\system32\MSVCP120D.dll 
File: C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\xtree 
Line: 1795 

Expression: invalid operator< 

For information on how your program can cause an assertion 
failure, see the Visual C++ documentation on asserts. 

(Press Retry to debug the application) 

--------------------------- 
Abort Retry Ignore 
--------------------------- 

为什么？

Answer 1

我会简单地使用由std::tie

bool operator < (const LocationData& other) const 
{ 
    return std::tie(mFileName, mDataSet, mChunkId, mAnimIndex) < std::tie(other.mFileName, other.mDataSet, other.mChunkId, other.mAnimIndex); 
} 

提供您可以重新排列成员为了在您需要逐一比较。

Answer 2

首先，您必须确定如何订购物品，然后您必须确保您的功能提供严格的弱顺序，而这不是您的功能所做的。

例如，你可以重写你的函数是这样的：

friend bool operator < (const LocationData& a, const LocationData& b) const 
{ 
    if (a.mFileName < b.mFileName)  // sort by filename... 
     return true; 
    else if (a.mFileName > b.mFileName) 
     return false; 
    else { 
     if (a.mDataSet < b.mDataSet)  // then by DataSet... 
      return true; 
     else if (a.mDataSet > b.mDataSet) 
      return false; 
     else { 
      if (a.mChunkId < b.mChunkId) 
       return true; 
      else if (a.mChunkId > b.mChunkId) 
       return false; 
      else 
       return a.mAnimIndex < b.mAnimIndex; 
     } 
    } 
}