使用 Boost Graph [BGL] 检查在 add_edge 之前是不是已经存在顶点

Posted 2023-02-21

【中文标题】使用 Boost Graph [BGL] 检查在 add_edge 之前是不是已经存在顶点

【英文标题】：Check if vertex already exists before an add_edge using Boost Graph [BGL]使用 Boost Graph [BGL] 检查在 add_edge 之前是否已经存在顶点

【发布时间】：2017-03-30 10:00:38

【问题描述】：

有没有办法检查使用 Boost 创建的图中的顶点是否已经存在，而不是循环遍历这些顶点？

如果它已经存在，我如何使用它的顶点描述符添加新边？

例子：

Graph g;
vertex v;

v = add_vertex(1, g);
vertex_name[v] = "root";

v = add_vertex(2, g);
vertex_name[v] = "vert_2";

v = add_vertex(3, g);
vertex_name[v] = "vert_3";

// This is not possible
edge e1;
if (vertex.find("root") == vertex.end()) 
   (boost::add_edge("root", "vert_2", g)).first

【问题讨论】：

vertex.find 是语法错误，什么意思？

【参考方案1】：

我想你可能会喜欢labeled_graph 适配器：

Live On Coliru

#include <iostream>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/labeled_graph.hpp>

using namespace boost;

int main()

    using AdjList = adjacency_list<setS, vecS, directedS>;
    using Graph = labeled_graph<AdjList, std::string, hash_mapS>;

    Graph g;

    for (std::string name :  "root", "vert_2", "vert_3" ) 
        add_vertex(name, g);
    

    struct  std::string from, to;  edges [] = 
        "root", "vert_2",
        "vert_2", "vert_3",
        "vert_2", "vert_3",
        "vert_2", "new_1",
        "new_1", "new_2",
    ;

    for (auto const& addition : edges) 
        if (g.vertex(addition.from) == g.null_vertex())
            std::cout << "source vertex (" << addition.from << ") not present\n";
        else if (g.vertex(addition.to) == g.null_vertex())
            std::cout << "target vertex (" << addition.to << ") not present\n";
        else 
            auto insertion = add_edge_by_label(addition.from, addition.to, g);
            std::cout << "Edge: (" << addition.from << " -> " << addition.to << ") "
                << (insertion.second? "inserted":"already exists")
                << "\n";
        
    

打印：

Edge: (root -> vert_2) inserted
Edge: (vert_2 -> vert_3) inserted
Edge: (vert_2 -> vert_3) already exists
target vertex (new_1) not present
source vertex (new_1) not present

【讨论】：

@Avi OT：coliru.stacked-crooked.com/a/e6efd0400c348981（回复您的deleted answer）