我使用boost::shared_ptr<Obj>
作为边缘属性的增强图的实现。我有两个课程Obj
和Obj2
,以便:
class Obj{
public:
Obj(){};
virtual func(){std::cout << "Obj func " << std::endl};
};
class Obj2: public Obj{
public:
Obj2(){};
virtual func(){std::cout << "Obj2 func " << std::endl};
};
我使用(简化)函数在图表中添加边缘,例如:
void addEdge(Vertex index, Vertex index2, const boost::shared_ptr<Obj>& edgeAttribute){
out = boost::add_edge(index, index2, edgeAttribute, graph).first;
}
我打电话使用:
Obj2* obj = new Obj2();
boost::shared_ptr<Obj2> obj_ptr(obj);
addEdge(index, index2, obj_ptr);
然而,稍后在我的代码中,通过执行edgeAttr = graph[edge]
然后调用函数edgeAttr->func()
来获取edge属性时,我会调用Obj的func而不是Obj2。
据我了解,这意味着我的对象被切片。这个简短的例子是我在使用boost:shared_ptr和BGL时应该切片我的对象,还是像初始化那样是我自己的其他一些实现问题?
答案 0 :(得分:1)
图形模型没有切片任何属性(注意,“属性”实际上称为捆绑属性)。
事实上,它永远不会复制 Obj
或Obj2
,因为它只会复制导致共享所有权的shared_ptr<>
,而不是复制属性
<强> Live On Coliru 强>
#include <boost/graph/adjacency_list.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/make_shared.hpp>
#include <iostream>
class Obj {
public:
Obj(){};
virtual void func(std::ostream& os) { os << "Obj func\n"; };
};
class Obj2 : public Obj {
public:
Obj2(){};
virtual void func(std::ostream& os) { os << "Obj2 func\n"; };
};
// I'm adding edges in the graph using a (simplified) function such as:
using Graph = boost::adjacency_list<boost::vecS, boost::vecS,
boost::directedS, boost::no_property, boost::shared_ptr<Obj> >;
using Vertex = Graph::vertex_descriptor;
struct Program {
Program() : _graph(10) {}
void addEdge(Vertex index, Vertex index2, const boost::shared_ptr<Obj> &edgeAttribute) {
auto out = boost::add_edge(index, index2, edgeAttribute, _graph).first;
}
void sample_edges() {
Obj2 *obj = new Obj2();
boost::shared_ptr<Obj2> obj_ptr(obj);
addEdge(1, 2, boost::make_shared<Obj2>());
addEdge(2, 3, boost::make_shared<Obj >());
addEdge(3, 4, boost::make_shared<Obj2>());
addEdge(4, 5, boost::make_shared<Obj >());
addEdge(5, 6, boost::make_shared<Obj2>());
addEdge(6, 7, boost::make_shared<Obj >());
}
void debug_dump() const {
for (auto ed : boost::make_iterator_range(boost::edges(_graph))) {
_graph[ed]->func(std::cout << "Edge " << ed << ": ");
}
}
private:
Graph _graph;
};
int main() {
std::cout << "Demo edges:\n";
Program demo;
demo.sample_edges();
demo.debug_dump();
std::cout << "Copied edges:\n";
// copy the whole shebang
Program clone = demo;
clone.debug_dump();
}
打印:
Demo edges:
Edge (1,2): Obj2 func
Edge (2,3): Obj func
Edge (3,4): Obj2 func
Edge (4,5): Obj func
Edge (5,6): Obj2 func
Edge (6,7): Obj func
Copied edges:
Edge (1,2): Obj2 func
Edge (2,3): Obj func
Edge (3,4): Obj2 func
Edge (4,5): Obj func
Edge (5,6): Obj2 func
Edge (6,7): Obj func