std :: set - 实现运算符的正确方法<！ - ？

Question

我有以下数据与运算符＆lt;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;
};

但是在使用std::set<LocationData>::insert时，我有时会收到以下消息：

---------------------------
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

首先，您必须确定如何订购商品，然后您必须确保您的功能提供严格的弱订单，而不是您的功能。

例如，您可以像这样重写您的函数：

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;
        }
    }
}

Answer 2

我只想使用std::tie

提供的词典比较

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

您可以根据需要重新排列成员订单。