我正在使用 boost::copy_graph
复制 adjacency_list
进入另一个adjacency_list
用不同的VertexProperties
模板。为此,我尝试使用 vertex_copy
参数(doc here)。我遇到了一个编译器错误,它告诉我第二个(待复制的)图的顶点属性类型错误。
最小示例
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/copy.hpp>
typedef boost::adjacency_list<boost::vecS,
boost::vecS,
boost::undirectedS,
uint32_t,
float> AdjacencyList;
typedef AdjacencyList::vertex_descriptor VertexID;
struct custom_property
{
uint32_t label;
float f;
};
typedef boost::adjacency_list<boost::vecS,
boost::vecS,
boost::undirectedS,
custom_property,
float> AdjacencyListCustom;
struct vertex_copier
{
void operator() (uint32_t &input, custom_property &output)
{
output.label = input;
output.f = 0.;
}
};
int main(int argc, char** argv)
{
AdjacencyList adj;
VertexID id_0 = boost::add_vertex(0, adj);
VertexID id_1 = boost::add_vertex(1, adj);
VertexID id_2 = boost::add_vertex(2, adj);
VertexID id_3 = boost::add_vertex(4, adj);
boost::add_edge(id_0, id_1, 1.0f, adj);
boost::add_edge(id_2, id_3, 2.0f, adj);
AdjacencyListCustom adj_custom;
boost::copy_graph(adj, adj_custom, boost::vertex_copy(vertex_copier()));
}
g++编译错误
...
/usr/include/boost/graph/copy.hpp:164:22: error: no match for call to '(vertex_copier) (boost::iterators::detail::iterator_facade_base<boost::range_detail::integer_iterator<long unsigned int>, long unsigned int, boost::iterators::random_access_traversal_tag, long unsigned int, long int, false, false>::reference, boost::graph_traits<boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, custom_property, float> >::vertex_descriptor&)'
copy_vertex(*vi, new_v);
~~~~~~~~~~~^~~~~~~~~~~~
/path/to/file.cpp: note: candidate: void vertex_copier::operator()(uint32_t&, custom_property&)
void operator() (uint32_t &input, custom_property &output)
^~~~~~~~
/path/to/file.cpp: note: no known conversion for argument 2 from 'boost::graph_traits<boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, custom_property, float> >::vertex_descriptor {aka long unsigned int}' to 'custom_property&'
这告诉我 vertex_copy
实际上是试图复制 vertex_descriptor
,这是一个 long unsigned int
, 不是 custom_property
.这似乎违背了文档中的说明:
这是一个二元函数,可将原始图中顶点的属性复制到拷贝中的相应顶点。
如何vertex_copy
工作?它可以用于在复制的图中设置/定义原始图中不存在的顶点属性吗?如果不是,是否必须在复制后通过遍历图形来设置这些属性?我可以整体应用映射还是必须访问和更新每个顶点?
编辑:
如果我尝试使用 copy_graph
未指定 vertex_copy
,然后出现错误,因为 =
custom_property
之间不存在运算符和 uint32_t
.
最佳答案
暂时回避这个问题,最简单的实现方法是向自定义属性添加适当的转换构造函数:
struct custom_property {
custom_property(uint32_t label = 0, float f = 0) : label(label), f(f) {}
uint32_t label;
float f;
};
在这种情况下,一个简单的拷贝就可以了:
boost::copy_graph(adj, adj_custom);
关于顶点复制器,它接收顶点描述符。要访问顶点属性,您需要有图形引用:
struct vertex_copier {
AdjacencyList& from;
AdjacencyListCustom& to;
void operator()(AdjacencyList::vertex_descriptor input, AdjacencyListCustom::vertex_descriptor output) const {
to[output] = { from[input], 0.f };
}
};
在这种情况下你会调用东西:
boost::copy_graph(adj, adj_custom, boost::vertex_copy(vertex_copier{adj, adj_custom}));
同样, Live On Coliru
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/copy.hpp>
#include <iostream>
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, uint32_t, float> AdjacencyList;
typedef AdjacencyList::vertex_descriptor VertexID;
struct custom_property {
//custom_property(uint32_t label = 0, float f = 0) : label(label), f(f) {}
uint32_t label;
float f;
};
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS, custom_property, float> AdjacencyListCustom;
struct vertex_copier {
AdjacencyList& from;
AdjacencyListCustom& to;
void operator()(AdjacencyList::vertex_descriptor input, AdjacencyListCustom::vertex_descriptor output) const {
to[output] = { from[input], 0.f };
}
};
int main(int argc, char **argv) {
AdjacencyList adj;
VertexID id_0 = boost::add_vertex(0, adj);
VertexID id_1 = boost::add_vertex(1, adj);
VertexID id_2 = boost::add_vertex(2, adj);
VertexID id_3 = boost::add_vertex(4, adj);
boost::add_edge(id_0, id_1, 1.0f, adj);
boost::add_edge(id_2, id_3, 2.0f, adj);
AdjacencyListCustom adj_custom;
boost::copy_graph(adj, adj_custom, boost::vertex_copy(vertex_copier{adj, adj_custom}));
}
关于c++ - boost::copy_graph 的vertex_copy 是如何工作的?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40442721/