c – 不能将std :: set of iterator中的元素插入到std :: list中

在显示给出编译器错误的代码之前,我想简要解释为什么我需要一组迭代器到列表,只是为了避免像“你真的需要吗？”这样的评论.或者可能将它们改为注释“你的代码可以用这种方式解决……但是我应该像这样解决原来的问题”.你可以跳过阅读并直接进入最后一节(“不编译代码”).

背后的原因

我构建了一个有向二分加权图.每个弧都存储在一个结构中

typedef struct edge_ {
    int src;
    int des;
    double w; //weight of the arc
}edge;

我使用这样的结构列表存储有关图形的信息.

list<edge> all_edges;

在那之后,我按重量对弧进行排序,然后将它们循环,从最轻到最重.
因为我想从循环中的all_edges中删除一些元素,所以在每个循环步骤的开始我调用

list<edge>::iterator smallest = all_edges.begin();

在该循环的每一步中,在完成了弧的权重之后,我想从图中删除所有从src离开或以des结尾的节点.为此,在构建图形的过程中,我创建了两个向量,一个用于二分图的每个组件,由它们的元素索引,并且在每个向量的每个位置,我将所有迭代器的列表存储到边缘all_edges,其离开与所考虑的向量的位置对应的节点.代码如下(“小”和“大”是我识别二分图的两个组成部分的方式)

vector<list<list<edge>::iterator>> edges_from_small(small.size());
vector<list<list<edge>::iterator>> edges_from_big(big.size());

这是我用来填充上述向量的代码

//inside a loop...
    edge e;
    e.src = ...
    e.des = ...
    e.w = ...
    all_edges.push_back(e);                
    edges_from_small[e.src].push_back(--(all_edges.end()));
    edges_from_big[e.des].push_back(--(all_edges.end()));

假设我要删除边缘e.
我很想循环edge_from_small [e.src]的所有元素,并为每个元素调用all_edges.erase(iterator),但这样做,因为边缘可以在edges_from_small和edges_from_big中列出,我会结束尝试使用解除引用的迭代器删除元素！

设置将是一个解决方案！我只需要创建一组list< edge> :: iterator并用edge_from_small [e.src]和edges_from_big [e.des]的元素填充它,然后,因为删除了重复项,删除所有元素从列表all_edges.

但我的代码没有编译,它给我一个我无法理解的错误,在以下某行之一：

set<list<edge>::iterator> to_remove;

for (auto it = edges_from_small[smallest->src].begin(); it != edges_from_small[smallest->src].end(); ++it) {
        to_remove.insert(*it); //error here! 
    }
for (auto it = edges_from_big[smallest->des].begin(); it != edges_from_big[smallest->des].end(); ++it) {
        //to_remove.insert(*it); //error here!
    }
for (auto it = to_remove.begin(); it != to_remove.end(); ++it) {
        all_edges.erase(*it);
    }

编译器为我提供了一个非常大的输出(都参考上面的行),目前我只放了第一行和最后一行,我认为这是最具指示性的.

g++ -ggdb3 -g -O0 -std=c++14 -Wall -Werror -o compare main.cpp peaks.cpp common.cpp compare.cpp parameters.cpp 
In file included from compare.cpp:1:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/iostream:38:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/ios:216:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/string:439:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/algorithm:628:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:606:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/iterator:344:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__functional_base:63:21: error: 
      invalid operands to binary expression ('const std::__1::__list_iterator<_edge,void *>' and 'const std::__1::__list_iterator<_edge,void *>')
        {return __x < __y;}
                ~~~ ^ ~~~
....................MUCH MORE OUTPUT....................
compare.cpp:226:23: note: in instantiation of member function
      'std::__1::set<std::__1::__list_iterator<_edge,void *>,std::__1::less<std::__1::__list_iterator<_edge,void *> >,std::__1::allocator<std::__1::__list_iterator<_edge,void *> > >::insert'
      requested here
            to_remove.insert(*it);
                      ^
1 error generated.
make: *** [compare] Error 1

Compilation exited abnormally with code 2 at Tue Sep  5 17:34:39

有关该线路有什么问题的任何想法？

不编译代码

typedef struct _edge {
    int src;
    int des;
    double w; //weight of the arch
}edge;

list<edge> all_edges;
vector<list<const list<edge>::iterator>> edges_from_small(small.size());
vector<list<const list<edge>::iterator>> edges_from_big(big.size());

//graph construction    
//for loop ...
    edge e;
    e.src = ...
    e.des = ...
    e.w = ... 
    all_edges.push_back(e);
    edges_from_small[e.src].push_back(--(all_edges.end())); 
    edges_from_big[e.des].push_back(--(all_edges.end()));
//end of loop

list<edge>::iterator smallest = all_edges.begin();
set<list<edge>::iterator> to_remove;
for (auto it = edges_from_small[smallest->src].begin(); 
     it != edges_from_small[smallest->src].end(); ++it) {
    to_remove.insert(*it); //<--- COMPILER ERROR HERE,you can see the error description in the last lines of the previous paragraph
}