Я новичок в C ++ и пытаюсь реализовать алгоритм Беллмана Форда,
моя программа не компилируется, я получаю следующую ошибку компилятора, которая довольно загадочная.
D:\ME\MCA\Sem2\LAB\DS\graph_algorithms>g++ bellman_ford.cpp -o bellman.exe
In file included from bellman_ford.cpp:8:0:
graph.h: In member function 'void Graph::print_distance_table()':
graph.h:172:31: error: passing 'const Vertex' as 'this' argument of 'char Vertex::get_name()' discards qualifiers
Файлы, которые я использую, представляют собой graph.h:
#ifndef GRAPH_H
#define GRAPH_H
class Vertex
{
private:
char vertex_name;
public:
Vertex(){};
Vertex(const char n)
{
vertex_name = n;
}
//Method signatures
char get_name();
//overloaded operators
bool operator==(Vertex other) const
{
if(vertex_name == other.get_name())
{
return true;
}
else return false;
}
bool operator< (Vertex other) const
{
if(vertex_name - other.get_name() < 0)
{
return true;
}
else return false;
}
};
class Edge
{
private:
Vertex source,destination;
int weight;
public:
Edge(){};
Edge(Vertex v1,Vertex v2,int w)
{
source = v1;
destination = v2;
weight = w;
}
//Method signatures
Vertex get_source();
Vertex get_destn();
int get_weight();
};
class Graph
{
private:
list<Vertex> V;
list<Edge> E;
map<Vertex,int> distances;
public:
Graph(list<Vertex> vertex_list,list<Edge> edge_list)
{
V = vertex_list;
E = edge_list;
}
// Method Signatures
bool add_vertex(Vertex);
bool remove_vertex(Vertex);
bool add_edge(Edge);
bool remove_edge(Edge);
int total_vertices();
int total_edges();
void initialize_distances(Vertex);
void print_distance_table();
};
/*
* Methods for the Vertex class are defined first
*/
char Vertex::get_name()
{
return vertex_name;
}
/*
* Methods for the Edge class are defined next
*/
int Edge::get_weight()
{
return weight;
}
Vertex Edge::get_destn()
{
return destination;
}
Vertex Edge::get_source()
{
return source;
}
/*
* Methods for our Graph class
*/
bool Graph::add_vertex(Vertex u)
{
V.push_back(u);
}
bool Graph::add_edge(Edge e)
{
E.push_back(e);
}
//slightly more tricky will write code when it'll be required i.e. when i implement dfs or some other algo
//that requires addition and removal of edges and vertices
bool Graph::remove_vertex(Vertex u)
{
//first check if it exists
//when a vertex is removed then then all the edges that have it as either a source or a destination should also be removed
}
//
bool Graph::remove_edge(Edge e)
{
//much easier than removing a vertex
//check if the edge exists and if it does remove it from the list..
}
int Graph::total_edges()
{
return E.size();
}
int Graph::total_vertices()
{
return V.size();
}
void Graph::initialize_distances(Vertex source)
{
distances.clear();
for(list<Vertex>::iterator it=V.begin(); it != V.end();it++)
{
//todo : overload = for the class vertex
if( *it == source)
{
distances[*it] = 0;
}
else
{
distances[*it] = INT_MAX;
}
}
}
void Graph::print_distance_table()
{
map<Vertex,int>::iterator mit;
for(mit = distances.begin(); mit != distances.end();mit++)
{
cout<<mit->first.get_name()<<"\t"<<mit->second<<endl;
}
}
#endif //GRAPH_H
и bellman_ford.cpp
#include<iostream>
#include<list>
#include<map>
#include<climits>
using namespace std;
#include "graph.h"
int main()
{
Graph G = Graph(list<Vertex>(), list<Edge>());
int vertices;
cout<<"Enter the no. of vertices : ";
cin>>vertices;
for(int i=0;i<vertices;i++)
{
cout<<"Enter the name of the vertex( one character only ) : ";
char tmp;
cin>>tmp;
Vertex tmp_vertex = Vertex(tmp);
G.add_vertex(tmp_vertex);
}
char choice;
do
{
char tmp_src,tmp_destn;
int tmp_w;
cout<<"Enter edge( source, destn, weight)";
cin>>tmp_src>>tmp_destn>>tmp_w;
G.add_edge( Edge(Vertex(tmp_src),Vertex(tmp_destn),tmp_w) );
cout<<"Add another edge (y|n)? ";
cin>>choice;
}while( choice != 'n');
Vertex source_vertex;
cout<<"\nEnter the source vertex : ";
cin>>choice;
source_vertex = Vertex(choice);
G.initialize_distances(source_vertex);
//now to iterate over the graph and compute the new shortest distances
G.print_distance_table();
return 0;
}
Я не очень знаком с картой stl, которая кажется источником ошибки в строке 172 файла graph.h.
если я удаляю ссылку на mit-> first.get_name (), то это работает, но я хочу также напечатать имена вершин.
Какая ошибка, которую я совершаю, дает эту ошибку?