Boost.Graph 和 Graphviz 嵌套子图

Question

我期待代码

#include <boost/graph/graphviz.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/subgraph.hpp>
#include <iostream>

using namespace boost;

using attrs_t = std::map<std::string, std::string>;

using graph_t = adjacency_list<
    vecS, vecS, directedS,
    property<vertex_attribute_t, attrs_t>,
    property<edge_index_t, int, property<edge_attribute_t, attrs_t>>,
    property<graph_name_t, std::string,
        property<graph_graph_attribute_t, attrs_t,
            property<graph_vertex_attribute_t, attrs_t,
                property<graph_edge_attribute_t, attrs_t>>>>>;

int main()
{
    char names[] = {"AB"};
    enum {A, B, N};

    subgraph<graph_t> main(N);
    subgraph<graph_t>& sub1 = main.create_subgraph();
    subgraph<graph_t>& sub2 = sub1.create_subgraph();

    add_vertex(A, sub1);
    add_vertex(B, sub2);
    add_edge(A, B, main);

    get_property(main, graph_name) = "G0";
    get_property(sub1, graph_name) = "clusterG1";
    get_property(sub2, graph_name) = "clusterG2";

    write_graphviz(std::cout, main, make_iterator_vertex_map(names));
}

生成左边的图表，而我得到了右边的：

输出是：

digraph G0 {
subgraph clusterG1 {
subgraph clusterG2 {
//B;
}
//A;
}
A -> B;
}

注释的节点语句是层次信息丢失的地方（我的输出中没有这些行）。我怎样才能避免这种情况？

---

如果我将两个顶点都添加到同一个子图中：

add_vertex(A, sub1);
add_vertex(B, sub1);
add_edge(A, B, main);

连接A -> B 出现在clusterG1 的范围内，根据我的理解，这就是所提到的顶点也将被隐式声明的地方。

我正在使用 Boost 1.68.0

Answer 1

好地方。正如您自己的回答所解释的那样，linked answer 实际上有 UB。传递给write_graphviz 函数的映射实际上不应该具有用于​​graphviz 输出的node_id。相反，该映射被假定为 vertex_index_t 属性映射。

这是我可能从boost::print_graph (graph_utility.hpp) 得出的一个假设，确实这样的属性映射。

为了使其安全工作，我将修改示例以使用 write_graphviz_dp - 使用动态属性：

int main() {
    boost::dynamic_properties dp;
    dp.property("node_id", boost::make_transform_value_property_map<std::string>(&name_for_index, boost::identity_property_map{}));
    write_graphviz_dp(std::cout, create_data<subgraph<Graph> >(), dp);
}

我选择使用转换函数来获取任何顶点描述符的名称，也不想再假设顶点的数量，我编写了更通用的函数来生成名称，例如“A”，...， "Z","AA",...,"ZZ" 等：

static std::string name_for_index(intmax_t index) {
    std::string name;

    do {
        name += 'A' + (index%26);
        index /= 26;
    } while (index);

    return name;
}

Live On Coliru

保留子图信息

上述重载不支持子图。因此，让我们修复 vertex_attribute 映射以具有预期的顶点标签：

int main() {
    auto g = create_data<subgraph<Graph> >();

    for (auto vd : make_iterator_range(vertices(g))) {
        put(get(vertex_attribute, g), vd, 
                GraphvizAttributes{
                    {"label", name_for_index(vd)}
                });
    }

    write_graphviz(std::cout, g);
}

现在它确实打印了：

Live On Coliru

digraph G0 {
subgraph clusterG1 {
graph [
label=G1];
node [
color=red, shape=Mrecord];
0[label="Vertex A"];
1[label="Vertex B"];
0 -> 1;
}
subgraph clusterG2 {
graph [
fillcolor=lightgray, label=G2, style=filled];
node [
shape=circle];
4[label="Vertex E"];
2[label="Vertex C"];
5[label="Vertex F"];
4 -> 5;
2 -> 5;
}
3[label="Vertex D"];
1 -> 2;
1 -> 3;
4 -> 1;
5 -> 3;
}

呈现为

完整列表

为后代保留

#include <boost/graph/graphviz.hpp>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/subgraph.hpp>
#include <iostream>

using namespace boost;

template <typename SubGraph> SubGraph create_data()
{
    enum { A,B,C,D,E,F,N }; // main edges
    SubGraph main(N);

    SubGraph& sub1 = main.create_subgraph();
    SubGraph& sub2 = main.create_subgraph();

    auto A1 = add_vertex(A, sub1);
    auto B1 = add_vertex(B, sub1);

    auto E2 = add_vertex(E, sub2);
    auto C2 = add_vertex(C, sub2);
    auto F2 = add_vertex(F, sub2);

    add_edge(A1, B1, sub1);
    add_edge(E2, F2, sub2);
    add_edge(C2, F2, sub2);

    add_edge(E, B, main);
    add_edge(B, C, main);
    add_edge(B, D, main);
    add_edge(F, D, main);

    // setting some graph viz attributes
    get_property(main, graph_name) = "G0";
    get_property(sub1, graph_name) = "clusterG1";
    get_property(sub2, graph_name) = "clusterG2";

    get_property(sub1, graph_graph_attribute)["label"]              = "G1";
    /*extra*/get_property(sub1, graph_vertex_attribute)["shape"]    = "Mrecord";

    get_property(sub2, graph_graph_attribute)["label"]              = "G2";
    /*extra*/get_property(sub1, graph_vertex_attribute)["color"]    = "red";
    /*extra*/get_property(sub2, graph_graph_attribute)["fillcolor"] = "lightgray";
    /*extra*/get_property(sub2, graph_graph_attribute)["style"]     = "filled";
    /*extra*/get_property(sub2, graph_vertex_attribute)["shape"]    = "circle";

    return main;
}

using GraphvizAttributes = 
    std::map<std::string, std::string>;

using Graph =
    adjacency_list<vecS, vecS, directedS, 
        property<vertex_attribute_t, GraphvizAttributes>,
        property<edge_index_t, int, property<edge_attribute_t, GraphvizAttributes> >,
        property<graph_name_t, std::string,
        property<graph_graph_attribute_t,  GraphvizAttributes,
        property<graph_vertex_attribute_t, GraphvizAttributes,
        property<graph_edge_attribute_t,   GraphvizAttributes>
        > > >
    >;

static std::string name_for_index(intmax_t index) {
    std::string name = "Vertex ";

    do {
        name += 'A' + (index%26);
        index /= 26;
    } while (index);

    return name;
}

int main() {
    auto g = create_data<subgraph<Graph> >();

    for (auto vd : make_iterator_range(vertices(g))) {
        put(get(vertex_attribute, g), vd, 
                GraphvizAttributes{
                    {"label", name_for_index(vd)}
                });
    }

    write_graphviz(std::cout, g);
}

Answer 2

问题是由提供make_iterator_vertex_map(names) 引起的，它从names（'A'，'B'）返回chars。这与预期的（和默认的）vertex_index 属性（0、1）不兼容。修复后，我得到：

digraph G0 {
subgraph clusterG1 {
subgraph clusterG2 {
1;
}
0;
}
0 -> 1;
}

vertex_marker，在我的例子中是std::vector<bool> 的2 元素，而不是67，并且预计更多元素会被顶点索引索引。我遇到了未定义的行为，
if ( vertex_marker[pos] ) 从未实现过。

boost::detail::write_graphviz_subgraph负责部分：

// Print out vertices and edges not in the subgraphs.

typename graph_traits<Graph>::vertex_iterator i, end;
typename graph_traits<Graph>::edge_iterator ei, edge_end;

for(boost::tie(i,end) = vertices(g); i != end; ++i) {
  Vertex v = g.local_to_global(*i);
  int pos = get(vertex_id, v); // 66, 65, should be 1, 0
  if ( vertex_marker[pos] ) {  // out-of-bounds access
    vertex_marker[pos] = false;
    out << escape_dot_string(pos);
    make_vertex_attributes_writer(g.root())(out, v);
    out << ";" << std::endl;
  }
}

vertex_id 参数类型的 static_assert/SFINAE 与 Graph 的 vertex_id 类型（可以立即在 boost::write_graphviz 中完成）将非常受欢迎。附带说明一下，硬编码的int pos = ... 看起来不太专业……

如果我们想保留自定义名称，我们必须改为通过label 属性提供它们。