Question

我正在开发一个包含类和函数模板的项目，我写了这些模板。在编译时我遇到了这个错误：

SNN.h In function `void KNN(const std::vector<T, std::allocator<_CharT> >&, std::vector<Cluster<T, K>, std::allocator<Cluster<T, K> > >&) [with T = int, unsigned int K = 5u]':

后面是这个错误（我认为它们是连接的）：

1)instantiated from `void ClusteringExample() [with T = int]'
2)instantiated from here:ClusteringExample<int>();
3)SNN.h [Warning] comparing floating point with == or != is unsafe
**4) conversion from `<unknown type>' to non-scalar type `__gnu_cxx::__normal_iterator<const Product*, std::vector<Product, std::allocator<Product> > >' requested**

当ClusteringExampke是func模板时。这是它的实施：

template <typename T>
void ClusteringExample()
    {
        std::vector<T> T_input;
        std::vector<Cluster<T,cluster_size> > clusters_T;
        FillVector( T_input, count_per_line );
        SNN( T_input, clusters_T);
        for (typename std::vector<Cluster<T,cluster_size> >::size_type i=0;       
    i<clusters_T.size(); i++ )
        {
            clusters_T[i].Print();
            std::cout << std::endl;
        }
        std::cout  << "===="<< std::endl; 
    }

KNN代码： **

void  KNN( const std::vector<T>& all_items, std::vector<Cluster<T,K> >& result )
{
     result.clear(); 
     if ( K > all_items.size() ) return; //we cannot create clusters bigger than the number of all items
     //for each item in all_items we will create a cluster
     for (typename std::vector<T>::size_type i=0; i < all_items.size(); i++ )
     {
         //this vector will save distances to the item i
         std::vector<double> distances;
         //passing over all items and calculating distance to the item i
         for (typename std::vector<T>::size_type j=0; j < all_items.size(); j++ )
         {
             distances.push_back( Distance(all_items[i], all_items[j] ));
         }
          //creating new cluster
         Cluster<T,K> new_cluster;
         //we are looking for K nearest distances
         std::sort( distances.begin(), distances.end() );
         for ( std::vector<double>::size_type d=0; d<K; d++ )
         {
              for (typename std::vector<T>::size_type j=0; j < all_items.size(); j++ )
               {
                  if (Distance(all_items[i], all_items[j] ) == distances[d] ) //every item which is closer then the "farest" is added to the cluster
                  {
                     new_cluster.Add( all_items[j] ); //we don't use the return value of Add in this implementation, but you need to support it
                  }
               }
         }
         result.push_back( new_cluster );

** 不得不说：它正在为我试图实例化的所有类型发生（int，double和类类型）。这个错误给我的信息量不大。任何人都可以找到问题所在的线索吗？

Answer 1

如果你真的有这个代码：

template<typename T, size_t K> void Cluster<T,K>::Print() const {
  for(typename vector<T>::const_iterator iter=_cluster_vec.begin;iter!=_cluster_vec.end();++iter) {
    cout<<(*iter)<<" "; 
  }
}

然后（a）您需要将begin更改为begin()并且（b）如果您在原始问题中发布了错误代码，那么您很快就会得到答案。

Answer 2

表达式Distance(all_items[i], all_items[j] ) == distances[d]可能会有一些令人惊讶的效果......您永远不应该将浮点数（float或double）与等式或不等式进行比较。

我建议您阅读IEEE 754标准并使用Google进行双重等同比较以获取更多信息。

此外，比较和评论似乎没有相关，你比较平等，但评论声称：

//every item which is closer then the "farest" is added to the cluster

也许你的意思是<=？

C ++：遇到func模板实例化问题

2 个答案: