Question

我正在尝试创建一个扩展boost图库行为的类。我希望我的类成为一个模板，用户提供一个类型（类），用于存储每个顶点的属性。那只是背景。我正在努力创建一个更简洁的typedef来用来定义我的新类。

基于this和this等其他帖子，我决定定义一个包含模板化typedef的结构。

我将展示两种密切相关的方法。我无法弄清楚为什么GraphType的第一个typedef似乎正在工作，而VertexType的第二个类型失败。

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

template <class VP>
struct GraphTypes
{
    typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, VP > GraphType;
    typedef boost::graph_traits< GraphType >::vertex_descriptor VertexType;
};

int main()
{
    GraphTypes<int>::GraphType aGraphInstance;
    GraphTypes<int>::VertexType aVertexInstance;
    return 0;
}

编译器输出：

$ g++ -I/Developer/boost graph_typedef.cpp 
graph_typedef.cpp:8: error: type ‘boost::graph_traits<boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, VP, boost::no_property, boost::no_property, boost::listS> >’ is not derived from type ‘GraphTypes<VP>’
graph_typedef.cpp:8: error: expected ‘;’ before ‘VertexType’
graph_typedef.cpp: In function ‘int main()’:
graph_typedef.cpp:14: error: ‘VertexType’ is not a member of ‘GraphTypes<int>’
graph_typedef.cpp:14: error: expected `;' before ‘aVertexInstance’

同样的，只是避免在第二个typedef中使用GraphType：

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

template <class VP>
struct GraphTypes
{
    typedef                      boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, VP > GraphType;
    typedef boost::graph_traits< boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, VP > >::vertex_descriptor VertexType;
};

int main()
{
    GraphTypes<int>::GraphType aGraphInstance;
    GraphTypes<int>::VertexType aVertexInstance;
    return 0;
}

编译器输出看起来效果相同：

g++ -I/Developer/boost graph_typedef.cpp 
graph_typedef.cpp:8: error: type ‘boost::graph_traits<boost::adjacency_list<boost::vecS, boost::vecS, boost::bidirectionalS, VP, boost::no_property, boost::no_property, boost::listS> >’ is not derived from type ‘GraphTypes<VP>’
graph_typedef.cpp:8: error: expected ‘;’ before ‘VertexType’
graph_typedef.cpp: In function ‘int main()’:
graph_typedef.cpp:14: error: ‘VertexType’ is not a member of ‘GraphTypes<int>’
graph_typedef.cpp:14: error: expected `;' before ‘aVertexInstance’

显然，第一个编译器错误是根本问题。我尝试在几个地方插入typename但没有成功。我正在使用gcc 4.2.1

我该如何解决这个问题？

Answer 1

typedef typename boost::graph_traits<GraphType>::vertex_descriptor VertexType;
//      ^^^^^^^^

应该修理它，我不知道你试图把它放在哪里..你可能还有其他问题我看不到。

使用boost图库的模板化typedef汤

1 个答案: