C++ Calculating Shortest Path in a Directed Graph - c++

Question

I am tasked with writing a program to maintain the representation of a simple network(weighted directed graph) and compute the best path between two given nodes upon request.
Currently, I am attempting to write a function to compute the simplest between two nodes, however, when attempting to run my program, I get two specific error
Severity Code Description Project File Line Suppression State
Error C3863 array type 'bool [openNode]' is not assignable P 127
and
Severity Code Description Project File Line Suppression State
Error C3863 array type 'int [openNode]' is not assignable
I am unable to debug since these two primary errors are not allowing my program to run. Is there any particular reason for these errors?
Thanks in advance!
This is the node structure defined in Graph.h
struct GraphNode
{
char ID;
std::string name;
int inNodes = 0;
int outNodes = 0;
std::vector<std::pair<GraphNode*, int>> connection;
int connections = 0;
};
And here is the particular code that causes the errors.
#include "Graph.h"
std::vector<GraphNode*> _graph;
int openNode = 0;
//Obligatory constructor
void Graph()
{
}
void shortestPath(char fromNode, char toNode)
{
bool known[openNode];
int distance[openNode];
GraphNode* previous[openNode];
int numbChecked = 0;
for (int i = 0; i < openNode; i++)
{
known[i] = false;
distance[i] = 999999;
previous[i] = nullptr;
}
distance[findNode(fromNode)] = 0;
while (numbChecked < openNode)
{
int smallestUnknown = 9999999;
int locationOfSmall = 0;
for (int i = 0; i < openNode; i++)
{
if (known[i] == false && distance[i] < smallestUnknown)
{
smallestUnknown = distance[i];
locationOfSmall = i;
}
}
if (distance[locationOfSmall] == 0)
{
previous[locationOfSmall] = nullptr;
}
known[locationOfSmall] = true;
numbChecked++;
if (_graph[locationOfSmall]->outNodes > 0)
{
for (int i = 0; i < _graph[locationOfSmall]->outNodes; i++)
{
int newDistanceLocation = findNode(_graph[locationOfSmall]->connection[i].first->ID);
if (known[newDistanceLocation] == false && (distance[locationOfSmall] + _graph[locationOfSmall]->connection[i].second) < distance[newDistanceLocation])
{
distance[newDistanceLocation] = distance[locationOfSmall] + _graph[locationOfSmall]->connection[i].second;
previous[newDistanceLocation] = _graph[locationOfSmall];
}
}
}
}
int destination = findNode(toNode);
std::string output;
std::string charTransfer;
charTransfer = toNode;
output = charTransfer;
while (previous[destination] != nullptr)
{
destination = findNode(previous[destination]->ID);
charTransfer = _graph[destination]->ID;
output = charTransfer + "->" + output;
}
if (_graph[destination]->ID != fromNode)
{
std::cout << "The nodes are not connected." << std::endl;
}
else
{
std::cout << "The path is: " << output << std::endl;
std::cout << "The distance is: " << distance[findNode(toNode)] << std::endl;
}
}
Any change suggestions would be much appreciated!

Answer 1

You have invalid code at the beginning of your shortestPath function:
bool known[openNode];
int distance[openNode];
GraphNode* previous[openNode];
You cannot use variables to create arrays on the stack (which is what you are trying to do there), because the compiler doesn't know the value of openNode at compile time (which is needed to determine the stack size).
Why don't you use a vector, like:
std::vector<bool> known(openNode, false);
std::vector<int> distance(openNode, 999999);
std::vector<GraphNode*> previous(openNode, nullptr);
Using this method makes the for loop below obsolete aswell.