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

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.

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