无法将 std::set 中的元素迭代器插入到 std::list

在显示给我编译器错误的代码之前，我想简要解释为什么我需要一组列表迭代器，只是为了避免像"你真的需要那个吗？"这样的评论，或者将它们更改为注释"你的代码可以用这种方式解决......但是，我应该像这样处理原始问题"。您可以跳过读取并直接转到最后一部分("未编译代码")。

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;

我使用此类结构的列表存储有关图形的信息。

list<edge> all_edges;

之后，我按重量对电弧进行排序，然后从最轻到最重循环。 由于我想从循环中的all_edges中删除一些元素，因此在每个循环步骤开始时，我调用

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

在该循环的每一步中，在用弧的重量做一些事情之后，我想从图中删除所有离开src或以des结尾的节点。为此，在图的构造过程中，我创建了两个向量，一个用于二分图的每个组件，按其元素进行索引，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all_edges的边缘，该边缘偏离与所考虑向量位置对应的节点。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()));

假设我想删除边缘e. 我很想循环edges_from_small[e.src]的所有元素，并让每个元素调用all_edges.erase(iterator)，但这样做，因为边可以在edges_from_small和edges_from_big中列出，我会结束尝试使用取消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edges_from_small[e.src]和edges_from_big[e.des]的元素填充它，然后，由于删除了重复项，因此从列表中删除所有元素all_edges。

但是我的代码无法编译，它给了我一个我无法理解的错误，在以下行之一：

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);
} 

编译器给了我一个相当大的输出(都引用了上面的行)，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

知道那条线有什么问题吗？

未编译代码

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
}