C++ std::sort() - 无法对访问成员变量的类类型的 vector 进行排序

Question

Entry.h:

//returns the sum of all non mega entry percentages
float sumOfNonMegaEntryPct(vector<Number>& arg1_Numbers);

Entry.cpp:

//returns the sum of all mega entry percentages
float Entry::sumOfMegaEntryPct(vector<MegaNumber>& arg1_MegaNumbers)
{
    float sumPct = 0.00f;
     for (MegaNumber c : megaEntry)
     {
         sumPct = sumPct + arg1_MegaNumbers[c.getID()].getOccurencePct();
     }

     return sumPct;
}

Lotto.h:

public:
//compares two entries, used for sorting algorithm, sorts by nonmega number
bool compareEntry_sumPct_nonMega(Entry arg1, Entry arg2); 

    protected:
    vector<Numbers> numbers;
    vector<MegaNumbers> megaNumbers;

Lotto.cpp:

#include "lotto.h"

//sorts nonmega numbers by sum of their pct, used for sort algorithm
bool Lotto::compareEntry_sumPct_nonMega(Entry arg1, Entry arg2)
{
    bool b = arg1.sumOfNonMegaEntryPct(numbers) < arg2.sumOfNonMegaEntryPct(numbers);
     return b;
}

源代码.cpp:

vector<Entry> copyGameEntry = game.getPlayEntry();
sort(copyGameEntry.begin(), copyGameEntry.end(),
     bind(&Lotto::compareEntry_sumPct_nonMega, game));

这只是代码的一部分，但我认为这足以说明问题。编译时出现错误:

Severity Code Description Project File Line Error C2451 conditional expression of type 'std::_Unforced' is illegal Lottery Sort e:\program files (x86)\microsoft visual studio 14.0\vc\include\algorithm 3133

Severity Code Description Project File Line Error C2675 unary '!': 'std::_Unforced' does not define this operator or a conversion to a type acceptable to the predefined operator Lottery Sort e:\program files (x86)\microsoft visual studio 14.0\vc\include\algorithm 3118

问题:

可能是什么问题？

Answer 1

您错误地使用了 std::bind。您需要为未绑定(bind)的参数使用占位符:

using namespace std::placeholders;
sort(copyGameEntry.begin(), copyGameEntry.end(),
     bind(&Lotto::compareEntry_sumPct_nonMega, game, _1, _2));

注意此绑定(bind)表达式将复制 game 对象，因此您应该使用 std::ref(game) 或仅使用 &game 来避免不必要的复制。

或者使用 lambda 函数:

sort(copyGameEntry.begin(), copyGameEntry.end(),
     [&game](Entry& l, Entry& r) {
       return game.compareEntry_sumPct_nonMega(l, r);
     });