std :: sort函子的聲明

Question

這是我的源代碼的外觀（簡化）：

class UncertaintyTest
{
private:
    class SpectralPeak
    {
    };

    std::list<SpectralPeak*> peaks;
};

struct SpectralPeakComparator
{
   bool operator()(const UncertaintyTest::SpectralPeak &a, const UncertaintyTest::SpectralPeak &b)
   {
      return a.TMiddleAvg() < b.TMiddleAvg();
   }
};

void UncertaintyTest::SortSpectralPeaks()
{
   std::sort(peaks.begin(), peaks.end(), SpectralPeakComparator());
}

編譯器拒絕編譯此源代碼，並出現以下錯誤：

 C2676: binary '-' : 'std::_List_iterator<_Mylist>' does not define this operator or a conversion to a type acceptable to the predefined operator   c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram
 C2780: 'void std::_Sort(_RanIt,_RanIt,_Diff)' : expects 3 arguments - 4 provided   c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram
 C2784: ''unknown-type' std::operator -(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'std::_List_iterator<_Mylist>'   c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram
 C2784: ''unknown-type' std::operator -(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'std::_List_iterator<_Mylist>' c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram
 C2784: ''unknown-type' std::operator -(std::move_iterator<_RanIt> &,const std::move_iterator<_RanIt2> &)' : could not deduce template argument for 'std::move_iterator<_RanIt> &' from 'std::_List_iterator<_Mylist>'  c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram
 C2784: 'std::complex<_Other> std::operator -(const _Ty &,const std::complex<_Other> &)' : could not deduce template argument for 'const std::complex<_Other> &' from 'std::_List_iterator<_Mylist>'    c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram
 C2784: 'std::complex<_Other> std::operator -(const std::complex<_Other> &,const _Ty &)' : could not deduce template argument for 'const std::complex<_Other> &' from 'std::_List_iterator<_Mylist>'    c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram
 C2784: 'std::complex<_Other> std::operator -(const std::complex<_Other> &,const std::complex<_Other> &)' : could not deduce template argument for 'const std::complex<_Other> &' from 'std::_List_iterator<_Mylist>'   c:\program files (x86)\microsoft visual studio 11.0\vc\include\algorithm    3868    1   Periodogram

有問題的行是std:sort 。 如果我發表評論，一切都很好。 我對比較器對象的聲明有什么問題？

Answer 1

問題是雙重的：

首先，排序函子不接受正確的值類型。 您的列表包含指針，而不是直接包含對象，因此比較函子也必須使用指針：

struct SpectralPeakComparator
{
   bool operator()(const UncertaintyTest::SpectralPeak *a, const UncertaintyTest::SpectralPeak *b)
   {
      return a->TMiddleAvg() < b->TMiddleAvg();
   }
};

其次， std::list沒有std::sort需要的隨機訪問迭代器。 您可以改為使用std::list::sort ：

peaks.sort(SpectralPeakComparator());