c++ - boost 图形库，depth_first_search 不在 msvc 中调用 finish_edge

Question

我在 vs-2017 中使用 Boost 1.70.0。使用 depth_first_search 时，我观察到访问者中的 finish_edge 函数在使用 msvc 编译器编译时未被调用。使用 gcc (8.3) 可以正确调用 finish_edge 函数

示例代码:

struct DfsVisitor : public boost::default_dfs_visitor
{
    template <class Graph>
    void
    finish_edge(typename Graph::edge_descriptor ed, const Graph& g)
    {
        std::cout << "Finish edge " << boost::source(ed, g) << "->" << boost::target(ed, g) << std::endl;
    }
};

DfsVisitor dfs;
boost::depth_first_search(g, boost::visitor(dfs)); // g is graph, adjacency_list

Answer 1

Do you have a SSCCE that we can actually run to observe the behavior? That will save a lot of time

我刚刚这样做了:刚刚这样做了:repro Boost 1.60 on msvc

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

struct DfsVisitor : public boost::default_dfs_visitor {
    template <class Graph> void finish_edge(typename Graph::edge_descriptor ed, const Graph &g) {
        std::cout << "Finish edge " << boost::source(ed, g) << "->" << boost::target(ed, g) << std::endl;
    }
};

int main() {
    boost::adjacency_list<> g(4);
    add_edge(0,1,g);
    add_edge(1,2,g);
    add_edge(2,3,g);

    DfsVisitor dfs;
    boost::depth_first_search(g, boost::visitor(dfs));

    std::cout << "Done\n";
}

只打印:

Done

为了比较，

• GCC 上的 Boost 1.58 也只打印 Done (https://rextester.com/GTFUY71911)

• Boost 1.70 在 GCC 9.1 上打印正确的输出:( https://godbolt.org/z/PMbEFL )

  Finish edge 2->3
  Finish edge 1->2
  Finish edge 0->1
  

很明显，它与 boost 版本的关系比与编译器的关系更大。 Godbolt 不会比 Boost 1.64 更早(仍然可以:https://godbolt.org/z/Ld8-8d)但 wandbox 可以:

• Boost 1.61.0 未打印预期信息 https://wandbox.org/permlink/ZSa2GMcZ1wrDtMVF
• Boost 1.62.0 执行:https://wandbox.org/permlink/tuup1N95iSk9rIfn

检查 release notes for Boost 1.62.0似乎没有提到什么，但使用 github 历史确实发现了:

$ git clone https://github.com/boostorg/graph
$ cd graph
$ git log --oneline --graph --left-right --cherry-pick boost-1.61.0...boost-1.62.0 | grep -i finish
> a14f8df8 Fixed bug 10231 partly: If finish_edge was called, then now correctly. (#16)
> d6b7a717 Add finish_edge test case from Alex Lauser.
> 6a2d45ae Condition TTI finish_edge on supported compilers.
> 0e1414f4 Fix type traits so finish_edge is called when defined.