Infinite loop when reading in input file?

Question

I get an infinite loop in the code while(input.find(' ', pos1) != string::npos)I created this code simply to read in the input via redirection and create a map of vertexes and a vector of characters for a graph. It's not very elegant so if you want to suggest a more effective way of reading in the input then that's good too. Thanks!

void MSTapp::processFile()
{
int pos1;
int pos2;
map<char, Vertex*> adjacencyList;
vector<char> listOrder;
string input;
bool test = false;
while (getline(cin, input)) {
    pos1 = pos2 = 0;
    if(std::string::npos != input.find_first_of("0123456789"))
    {

        char source = input[0];
        char destination = input[2];
        stringstream ss(input.substr(4));       
        int weight;
        ss >> weight;
        Edge newEdge(destination, weight);
        adjacencyList[source]->addEdge(destination, newEdge);
        Edge roadBack(source, weight);
        adjacencyList[destination]->addEdge(source, roadBack);
    }
    else
    {
        while(input.find(' ', pos1) != string::npos)
        {
            pos2 = input.find(' ', pos1);
            char vertex = input[pos1];
            listOrder.push_back(vertex);
            Vertex* newVertex = new Vertex(vertex);
            adjacencyList.insert(make_pair(vertex, newVertex));
            pos1 = pos2 + 1;
        };
    };
};
Graph graph(listOrder, adjacencyList);
prim(graph, adjacencyList[listOrder[0]]);
}

Input

A B C D E F G
A B 3
A E 4
B C 7 
B E 6
B F 5
C D 9
C F 8
D F 9
D G 4
E F 6
F G 8

elixenide · Accepted Answer · 2013-12-16 22:47:44Z

3

Here's the problem:

while(input.find(' ', pos1) != string::npos)
    {
        pos2 = input.find(' ', pos1);
        char vertex = input[pos1];
        listOrder.push_back(vertex);
        Vertex* newVertex = new Vertex(vertex);
        adjacencyList.insert(make_pair(vertex, newVertex));
        pos1 = pos2;
    };

Change pos1 = pos2; to pos1 = pos2+1; -- it never moves, so the while loop never ends.

You also need to make sure pos1 < string::length in your while condition.

edited Dec 16, 2013 at 22:47

answered Dec 16, 2013 at 22:36

elixenide

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