在'{'token'之前不允许使用function-definition

Question

我在我的qt项目m中包含了“Edge_collapse_recorder.h”，我想在折叠过程中打印一些值，但是当我取消注释std :: cout <<“collapse edge”<< profile.v0_v1（）<<“”时它会显示以下错误<< << profile.v0（）<<“”<< profile.v1（）<< std :: endl;线：

../CM2/edge_collapse_recorder.h:102:37: error: no match for ‘operator<<’ (operand types are ‘std::basic_ostream<char>’ and ‘const halfedge_descriptor’ {aka ‘const CGAL::internal::CC_iterator<CGAL::Compact_container<CGAL::Dart<2, CGAL::CMap_linear_cell_complex_storage_1<2, 3, CGAL::Linear_cell_complex_traits<3, CGAL::Simple_cartesian<double> >, CGAL::Linear_cell_complex_bgl_min_items, std::allocator<int> >, CGAL::Void, CGAL::Boolean_tag<true> >, std::allocator<CGAL::Dart<2, CGAL::CMap_linear_cell_complex_storage_1<2, 3, CGAL::Linear_cell_complex_traits<3, CGAL::Simple_cartesian<double> >, CGAL::Linear_cell_complex_bgl_min_items, std::allocator<int> >, CGAL::Void, CGAL::Boolean_tag<true> > >, CGAL::Default, CGAL::Default>, false>’})
       std::cout << "collapse edge " << profile.v0_v1() << " " << << profile.v0()  << " " << profile.v1() << std::endl;
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~

我搜索了这个问题，发现我必须重载<<运算符，然后我将以下内容添加到onCollapssing方法：

 std::ostream& operator<<(std::ostream& os, const Edge_collapse_recorder& t) {
                      os <<  << "collapse edge " << t.v0_v1() << " " << << t.v0()  << " " << t.v1();
                     return os;
                 }

但它显示以下错误：'{'token'之前不允许使用函数定义

  void OnCollapsing(Profile const& profile
                      ,boost::optional<Point_3>  placement
                      )
    {
      visitor.OnCollapsing(profile,placement);

      if ( placement ){
           std::ostream& operator<<(std::ostream& os, const Edge_collapse_recorder& t) {
                     os <<  << "collapse edge " << t.v0_v1() << " " << << t.v0()  << " " << t.v1();
                     return os;
                 }

        Record record;
        record.v0 = profile.v0();
        record.v1 = profile.v1();
        record.p0 = profile.p0();
        record.p1 = profile.p1();
        halfedge_descriptor hd = profile.v0_v1();

        record.oppa = (! is_border(hd,recorder.sm))
          ? target(next(hd, recorder.sm),recorder.sm)
          : boost::graph_traits<LCC>::null_vertex();

        record.oppb = (! is_border(opposite(hd, recorder.sm),recorder.sm))
          ? target(next(opposite(hd, recorder.sm), recorder.sm),recorder.sm)
          : boost::graph_traits<LCC>::null_vertex();

        recorder.records.push_back(record);
      }
    }

Answer 1

那个注释掉的行永远不会编译。它有两个连续的<<运营商。

至于错误消息，您正在定义该函数

std::ostream& operator<<(std::ostream& os, const Edge_collapse_recorder& t)

（而不仅仅是声明它）在另一个函数中。 C++中不允许嵌套函数定义。要做你想做的事（我不确定这是不是一个好主意），把函数定义放在OnCollapsing函数之前。