读取输入文件时的无限循环？ [英] Infinite loop when reading in input file?

问题描述

我在代码中得到一个无限循环 while（input.find（''，pos1）！= string :: npos）通过重定向的输入并创建顶点的映射和图形的字符的向量。它不是很优雅，所以如果你想建议一个更有效的方式阅读输入，那么这也是好的。感谢！

  void MSTapp :: processFile（）
 {
 int pos1; 
 int pos2; 
 map< char，Vertex *> adjacencyList; 
矢量< 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>>重量; 
 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; 
}; 
}; 
}; 
图形图表（listOrder，adjacencyList）; 
 prim（graph，adjacencyList [listOrder [0]]）; 
} 
  

输入

  ABCDEFG 
 AB 3 
 AE 4 
 BC 7 
 BE 6 
 BF 5 
 CD 9 
 CF 8 
 DF 9 
 DG 4 
 EF 6 
 FG 8 
  

这里的问题：

  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; 
}; 
  

更改 pos1 = pos2; 至 pos1 = pos2 + 1; - 它从不移动，因此 while b

您还需要确保 pos1< while 条件下的字符串:: length 。

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

解决方案

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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