Question

我正在努力从我的图表中删除所有节点（使用定义为here的模式），这些节点没有连接边缘。到目前为止，我的（MWE）代码如下：

if (!function_exists('mh_featured_image')) {
    function mh_featured_image() {
        global $post;
        if (has_post_thumbnail() && !is_attachment()) {
            $thumbnail = wp_get_attachment_image_src(get_post_thumbnail_id(), 'content');
            // echo "\n" . '<div class="post-thumbnail">' . "\n";
            //  echo '<img src="' . esc_url($thumbnail[0]) . '" alt="' . esc_attr(get_post_meta(get_post_thumbnail_id(), '_wp_attachment_image_alt', true)) . '" title="' . esc_attr(get_post(get_post_thumbnail_id())->post_title) . '" />' . "\n";
            //  if (get_post(get_post_thumbnail_id())->post_excerpt) {
            //      echo '<span class="wp-caption-text">' . esc_attr(get_post(get_post_thumbnail_id())->post_excerpt) . '</span>' . "\n";
            //  }
            // echo '</div>' . "\n";
        }
    }
   }

不幸的是，代码在与投诉的汇编中出错：

//g++ -O3 question.cpp -o question.exe
#include <iostream>

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

typedef long long node_id_t;

typedef boost::adjacency_list<
  boost::listS,           // Store out-edges of each vertex in a std::list
  boost::listS,           // Store vertex set in a std::list
  boost::bidirectionalS,  // The file dependency graph is directed
  boost::no_property,     // vertex properties
  boost::no_property      // edge properties
> AdjGraph;

typedef boost::labeled_graph<
  AdjGraph,
  node_id_t          // Node ID
> LabeledGraph;

int main(){
  LabeledGraph g;

  add_vertex( 10, g );
  add_vertex( 20, g );
  add_vertex( 30, g );
  add_vertex( 40, g );
  add_vertex( 50, g );

  boost::graph_traits<LabeledGraph>::vertex_iterator vi, vi_end, next;
  boost::tie(vi, vi_end) = boost::vertices(g);
  for (next = vi; vi != vi_end; vi = next) {
    ++next;
    if(boost::degree(*vi)==0)
      boost::remove_vertex(*vi, g);
  }
}

我的期望是question.cpp:36:25: error: no matching function for call to ‘degree(void*&)’ if(boost::degree(*vi)==0)是vi，解除引用它应该给我一个有效的描述符。我不确定为什么这不会发生。

我怎样才能做到这一点？

Answer 1

您需要传递extra argument g to degree()。

此外，由于LabeledGraph适配器未对MutableGraph进行建模，remove_vertex调用无效。

幸运的是，你可以获得基础图并改变它。我必须阅读LabeledGraph以了解是否存在不利影响：

<强> Live On Coliru

// g++ -O3 question.cpp -o question.exe
#include <iostream>

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

typedef long long node_id_t;

typedef boost::adjacency_list<boost::listS,          // Store out-edges of each vertex in a std::list
                              boost::listS,          // Store vertex set in a std::list
                              boost::bidirectionalS, // The file dependency graph is directed
                              boost::no_property,    // vertex properties
                              boost::no_property     // edge properties
                              > AdjGraph;

typedef boost::labeled_graph<AdjGraph,
                             node_id_t // Node ID
                             > LabeledGraph;

int main() {
    LabeledGraph g;

    add_vertex(10, g);
    add_vertex(20, g);
    add_vertex(30, g);
    add_vertex(40, g);
    add_vertex(50, g);

    boost::graph_traits<LabeledGraph>::vertex_iterator vi, vi_end, next;

    AdjGraph& underlying = g.graph();

    boost::tie(vi, vi_end) = boost::vertices(underlying);
    for (next = vi; vi != vi_end; vi = next) {
        ++next;
        if (boost::degree(*vi, underlying) == 0)
            boost::remove_vertex(*vi, underlying);
    }
}

也许你可以不用LabeledGraph：

<强> Live On Coliru

// g++ -O3 question.cpp -o question.exe
#include <iostream>

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graph_utility.hpp>

typedef long long node_id_t;

typedef boost::adjacency_list<boost::listS,          // Store out-edges of each vertex in a std::list
                              boost::listS,          // Store vertex set in a std::list
                              boost::bidirectionalS, // The file dependency graph is directed
                              node_id_t,             // vertex properties
                              boost::no_property     // edge properties
                              > AdjGraph;

int main() {
    AdjGraph g;

               add_vertex(10, g);
    auto v20 = add_vertex(20, g);
               add_vertex(30, g);
    auto v40 = add_vertex(40, g);
               add_vertex(50, g);

    add_edge(v40, v20, g);

    std::cout << "BEFORE:\n";
    print_graph(g, boost::get(boost::vertex_bundle, g));

    boost::graph_traits<AdjGraph>::vertex_iterator vi, vi_end, next;

    boost::tie(vi, vi_end) = boost::vertices(g);
    for (next = vi; vi != vi_end; vi = next) {
        ++next;
        if (boost::degree(*vi, g) == 0)
            boost::remove_vertex(*vi, g);
    }

    std::cout << "\n---\nAFTER:\n";
    print_graph(g, boost::get(boost::vertex_bundle, g));
}

打印：

BEFORE:
10 --> 
20 --> 
30 --> 
40 --> 20 
50 --> 

---
AFTER:
20 --> 
40 --> 20

BGL中的顶点迭代度

1 个答案: