如何在 C++ 中的 Map 中存储 cv::Scalar 对象

Question

我想将随机生成的标量值存储在地图中。但是下面的尝试给了我一个编译错误。

RNG rng(0xFFFFFFFF);
std::map<Scalar, int> segmentColors;

Scalar randomColorTemp1 = randomColor(rng);
Scalar randomColorTemp2 = randomColor(rng);

segmentColors.insert(pair<Scalar, int>(randomColorTemp1, 1));
segmentColors.insert(pair<Scalar, int>(randomColorTemp1, 1));

报错如下。

1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xstddef(193): error C2678: binary '<' : no operator found which takes a left-hand operand of type 'const cv::Scalar' (or there is no acceptable conversion)
1>          e:\opencv\build\include\opencv2\core\operations.hpp(3193): could be 'bool cv::operator <(const cv::FileNodeIterator &,const cv::FileNodeIterator &)' [found using argument-dependent lookup]
1>          e:\opencv\build\include\opencv2\core\mat.hpp(1303): or       'cv::MatExpr cv::operator <(const cv::Mat &,const cv::Mat &)' [found using argument-dependent lookup]
1>          e:\opencv\build\include\opencv2\core\mat.hpp(1304): or       'cv::MatExpr cv::operator <(const cv::Mat &,double)' [found using argument-dependent lookup]
1>          e:\opencv\build\include\opencv2\core\mat.hpp(1305): or       'cv::MatExpr cv::operator <(double,const cv::Mat &)' [found using argument-dependent lookup]
1>          e:\opencv\build\include\opencv2\core\mat.hpp(1984): or       'bool cv::operator <(const cv::MatConstIterator &,const cv::MatConstIterator &)' [found using argument-dependent lookup]
1>          while trying to match the argument list '(const cv::Scalar, const cv::Scalar)'
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xstddef(192) : while compiling class template member function 'bool std::less<_Kty>::operator ()(const _Ty &,const _Ty &) const'
1>          with
1>          [
1>              _Kty=cv::Scalar
1>  ,            _Ty=cv::Scalar
1>          ]
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\map(228) : see reference to function template instantiation 'bool std::less<_Kty>::operator ()(const _Ty &,const _Ty &) const' being compiled
1>          with
1>          [
1>              _Kty=cv::Scalar
1>  ,            _Ty=cv::Scalar
1>          ]
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\type_traits(572) : see reference to class template instantiation 'std::less<_Kty>' being compiled
1>          with
1>          [
1>              _Kty=cv::Scalar
1>          ]
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xtree(1023) : see reference to class template instantiation 'std::is_empty<std::less<_Kty>>' being compiled
1>          with
1>          [
1>              _Kty=cv::Scalar
1>          ]
1>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\map(70) : see reference to class template instantiation 'std::_Tree<std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,false>>' being compiled
1>          with
1>          [
1>              _Kty=cv::Scalar
1>  ,            _Ty=int
1>  ,            _Pr=std::less<cv::Scalar>
1>  ,            _Alloc=std::allocator<std::pair<const cv::Scalar,int>>
1>          ]
1>          g:\uom\level 4-s1\research project\coding tests\textextraction\textextraction\source1.cpp(288) : see reference to class template instantiation 'std::map<cv::Scalar,int,std::less<_Kty>,std::allocator<std::pair<const _Kty,_Ty>>>' being compiled
1>          with
1>          [
1>              _Kty=cv::Scalar
1>  ,            _Ty=int
1>          ]
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

有人可以找出我的代码中的错误或提供更好的方法来将随机生成的标量颜色值存储在地图中吗？将它们存储在地图中的目的是避免生成重复的颜色值。我想防止生成相似的 RGB 值。

---

更新

---

根据 berak 的回答，我尝试了这个。

---

    RNG rng(0xFFFFFFFF);
    struct ScalarLess
    {
        bool operator()(Scalar &a, Scalar &b)
        {
            return a[0] < b[0]; // bogus, i doubt, that you need *real* sorting
        }
    };
    Scalar randomColorTemp = randomColor(rng);
    map<Scalar, int, ScalarLess> segmentColorsMap;
    segmentColorsMap.insert((pair<Scalar, int>(randomColorTemp, 2)));

Answer 1

如果您希望 Scalar 作为地图的键，您需要提供“Less”运算符，以便对其进行排序。像这样：

struct ScalarLess
{
   bool operator()(const Scalar &a, const Scalar &b)
   {
       return a[0] < b[0]; // bogus, i doubt, that you need *real* sorting
   }
};


map<Scalar,int,ScalarLess> segmentColors;