具有给出三角形网格的连通分量的函数的奇怪错误

Question

我正在尝试在 C++ 中编写一个函数，该函数为我提供了三角形网格的连通分量。我有一个自定义的 class，它可以对 3D 三角形网格进行建模。我的目标是获得一个 std::vector<Mesh2d> ，每个组件都包含我的网格的一个连接组件。

class Mesh2d{
    
    std::vector<R3>* node_ptr;
    std::vector<Elt2d> elt;
public:
    
    Mesh2d(){};
    Mesh2d(std::vector<R3>& node){}
    void Load(const string& filename){}
    void PushBack(const Elt2d& e){}
    std::vector<Elt2d>::iterator begin(){}
    std::vector<Elt2d>::iterator end(){}
    std::vector<int> Num(const int& j) const {}
    void Plot(string filename) const {}
    const Elt2d& operator[](const int& j) const {}
    std::vector<Elt2d> const GetElt() const {}
    void GetBoundary(Mesh& mesh){} 
    friend  std::vector<Elt2d> adj(Elt2d e, Mesh2d mesh){}
    friend int find_index(Elt2d e,Mesh2d mesh){}
    

    friend void DFS(int j , std::vector<bool> visited, Mesh2d boundary, std::vector<Mesh2d> ConnectedComponents, int n){
         visited[j] = true;

        std::cout<<"visited = " << visited << std::endl;
        ConnectedComponents[n].PushBack(boundary[j]);
        Elt2d e = boundary[j];
        std::vector<Elt2d> neighbor = adj(e,boundary);
        for(int i = 0; i<neighbor.size(); ++i){
         //   std::cout<<"i = " << i << std::endl;
            int p = find_index(neighbor[i], boundary);
            if(visited[p] == false){
                DFS(p, visited, boundary, ConnectedComponents, n);
            }
            
             
            
        }
    }


    std::vector<Mesh2d> Boundary(Mesh mesh){
        Mesh2d boundary;
        boundary.GetBoundary(mesh);
        std::vector<Mesh2d> ConnectedComponents;
        std::vector<bool> visited(boundary.NbElt(),false);
        std::vector<bool> True(boundary.NbElt(),true);
        int k = 0;
        for(int j = 0; j<boundary.NbElt(); ++j){
            ConnectedComponents.resize(k+1);
            std::cout<<"j =" << j << std::endl;
            Elt2d e = boundary[j];
            if(visited[j]==false){

                DFS(j, visited, boundary, ConnectedComponents,k);
                ConnectedComponents[k].PushBack(boundary[j]);
                std::cout<< "NbCC = " << ConnectedComponents.size() << std::endl;
                
            
            



            }

            ++k;
           std::cout<<"k = " << k << std::endl;
            
        }
        return ConnectedComponents;
    }
};

其中 R3 和 Elt2d 是自定义的 class，表示 3D 向量和三角形。我的问题是两个函数 DFS 和 Boundary，我正在使用深度优先搜索算法来探索我的网格（以三角形作为节点）。但是我遇到了一个奇怪的错误，我的向量 visited 将其某些值更改为 false。如果我为一个小网格打印我的 visited 矢量，我得到这个：

visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   0   1   1   1   1   1   1   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   0   0   1   1   1   1   0   1
visited = 1 1   1   1   1   0   1   1   1   1   0   1
visited = 1 1   1   1   1   1   1   1   1   1   0   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   1   0   1   1   1   1   1   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   0   1   1   1   1   1   0   1
visited = 1 1   1   1   1   1   1   1   1   1   0   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   0   1   1   1   1   1   1   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   0   0   1   1   1   1   1   1
visited = 1 1   1   1   1   0   1   1   1   1   1   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   0   1   1   1   1   1   1   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   0   0   1   1   1   0   1   1
visited = 1 1   1   1   1   0   1   1   1   0   1   1
visited = 1 1   1   1   1   1   1   1   1   0   1   1
visited = 1 1   1   1   1   1   1   1   1   1   1   1
visited = 1 1   1   1   1   0   1   1   1   1   1   1

我完全不知道为什么会这样。请记住，我是 C++ 的初学者，我的代码的某些部分（或大部分）看起来很傻。任何帮助将不胜感激

Answer 1

您正在按值传递 visited：

void DFS(int j, std::vector<bool> visited, Mesh2d boundary, std::vector<Mesh2d> ConnectedComponents, int n)

这意味着每次调用 DFS 函数时都会复制此向量，并且不会更改原始向量的值。您观察到当您从函数中 return 时值“恢复”。

改为通过引用传递向量：

void DFS(int j, std::vector<bool> &visited, Mesh2d &boundary, std::vector<Mesh2d> &ConnectedComponents, int n)

修改其余代码，您永远不会通过引用传递“重”对象。那至少是低效的。

具有给出三角形网格的连通分量的函数的奇怪错误

Weird bug with a function that gives the connected component of a triangular mesh

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mesh