I don't know where the error is coming from. It seems like I'm passing valid data into the [ ] operator.
我不知道错误来自哪里。好像我将有效数据传递给[]运算符。
template <class VertexType>
typename map< Vertex<VertexType>, int >::iterator Graph<VertexType>::findEdge( const VertexType& v, const VertexType& w ) const
{
map<Vertex<VertexType>, int>::const_iterator iter = vertices[v].second.adjList.find(w);
return iter;
} // end findEdge
The error:
error C2678: binary '[' : no operator found which takes a left-hand operand of type 'const std::map<_Kty,_Ty>' (or there is no acceptable conversion)
1> with
1> [
1> _Kty=unsigned int,
1> _Ty=Vertex<unsigned int>
1> ]
1> c:\program files (x86)\microsoft visual studio 10.0\vc\include\map(164): could be 'Vertex<VertexType> &std::map<_Kty,_Ty>::operator [](unsigned int &&)'
1> with
1> [
1> VertexType=unsigned int,
1> _Kty=unsigned int,
1> _Ty=Vertex<unsigned int>
1> ]
1> c:\program files (x86)\microsoft visual studio 10.0\vc\include\map(209): or 'Vertex<VertexType> &std::map<_Kty,_Ty>::operator [](const unsigned int &)'
1> with
1> [
1> VertexType=unsigned int,
1> _Kty=unsigned int,
1> _Ty=Vertex<unsigned int>
1> ]
1> while trying to match the argument list '(const std::map<_Kty,_Ty>, const unsigned int)'
1> with
1> [
1> _Kty=unsigned int,
1> _Ty=Vertex<unsigned int>
1> ]
1> c:\users\user\desktop\cs m20a\topic g project 2\topic g project 2\graph.h(146) : while compiling class template member function 'std::_Tree_iterator<_Mytree> Graph<VertexType>::findEdge(const VertexType &,const VertexType &) const'
1> with
1> [
1> _Mytree=std::_Tree_val<std::_Tmap_traits<Vertex<unsigned int>,int,std::less<Vertex<unsigned int>>,std::allocator<std::pair<const Vertex<unsigned int>,int>>,false>>,
1> VertexType=unsigned int
1> ]
1> c:\users\user\desktop\cs m20a\topic g project 2\topic g project 2\graph.h(52) : while compiling class template member function 'Graph<VertexType>::Graph(unsigned int)'
1> with
1> [
1> VertexType=unsigned int
1> ]
1> c:\users\user\desktop\cs m20a\topic g project 2\topic g project 2\topicg.cpp(17) : see reference to class template instantiation 'Graph<VertexType>' being compiled
1> with
1> [
1> VertexType=unsigned int
1> ]
And the Graph class:
而Graph类:
template <class VertexType>
class Graph
{
private:
// list of all vertices in the graph. assumes non-duplicate data.
map< VertexType, Vertex<VertexType> > vertices;
const unsigned MAX_VERTICES; // Maximum number of vertices the graph can hold.
unsigned numVertices; /** Current number of vertices in the graph. */
unsigned numEdges; /** Number of edges in the graph. */
typename map< Vertex<VertexType>, int >::iterator findEdge( const VertexType& v, const VertexType& w ) const;
public:
Graph( unsigned max );
unsigned getNumVertices() const;
unsigned getMaxNumVertices() const;
unsigned getNumEdges() const;
int getWeight( const VertexType& v, const VertexType& w ) const;
Graph<VertexType>& addVertex( const VertexType& newValue );
Graph<VertexType>& addEdge( const VertexType& v, const VertexType& w, int weight );
void removeEdge( const VertexType& v, const VertexType& w );
void BFS( const VertexType& v ) const;
void display() const;
}; // end Graph
2 个解决方案
#1
35
operator[] can only be called on a non-const map.
operator []只能在非const映射上调用。
If the key doesn't exist, it will be inserted with a default constructed value.
如果密钥不存在,则将使用默认构造值插入密钥。
To get a const iterator, use map::find.
要获取const迭代器,请使用map :: find。
#2
2
While not the case above, the same problem will occur if you use the [] operator in a const function.
虽然不是上述情况,但如果在const函数中使用[]运算符,也会出现同样的问题。
#1
35
operator[] can only be called on a non-const map.
operator []只能在非const映射上调用。
If the key doesn't exist, it will be inserted with a default constructed value.
如果密钥不存在,则将使用默认构造值插入密钥。
To get a const iterator, use map::find.
要获取const迭代器,请使用map :: find。
#2
2
While not the case above, the same problem will occur if you use the [] operator in a const function.
虽然不是上述情况,但如果在const函数中使用[]运算符,也会出现同样的问题。