如何在迭代boost :: Intrusive :: list时擦除

How to erase while iterating boost::intrusive::list

本文关键字：Intrusive list 擦除 boost 迭代      更新时间：2023-10-16

在迭代过程中如何从 boost::intrusive::list中删除元素？主张失败https://wandbox.org/permlink/nzfshfssairvbita

，以下代码失败了 
#include <iostream>
#include <vector>
#include <boost/intrusive/list.hpp>
using std::cout;
using std::endl;
class Integer : public boost::intrusive::list_base_hook<> {
public:
    explicit Integer(int a_in) : a{a_in} {}
    int a;
};
int main() {
    auto vec = std::vector<Integer>{};
    vec.push_back(Integer{1});
    vec.push_back(Integer{2});
    vec.push_back(Integer{3});
    auto list = boost::intrusive::list<Integer>{};
    for (auto ele : vec) {
        list.push_back(ele);
    }
    for (auto it = list.begin(); it != list.end();) {
        if (it->a == 2) {
            it = list.erase(it);
        } else {
            ++it;
        }
    }
    for (auto ele : list) {
        cout << ele.a << endl;
    }
}

您的问题是您已将临时工推入列表：

for (auto ele : vec) {
    list.push_back(ele);
}

您可能打算写：

for (auto& ele : vec) {
    list.push_back(ele);
}

这是 classic 开始使用侵入容器时的混乱：没有像所有标准库容器那样按价值划分的价值。

要避免这样的情况，请考虑使用自动链接挂钩模式。

demo

甚至比不必考虑参考循环变量更安全，根本没有循环：

boost::intrusive::list<X> list(vec.begin(), vec.end());

活在coliru 

#include <iostream>
#include <iterator>
#include <vector>
#include <boost/intrusive/list.hpp>
struct X : public boost::intrusive::list_base_hook<> {
    X(int a_in) : a{a_in} {}
    int a;
    friend std::ostream& operator<<(std::ostream& os, X const& x) { return os << "{" << x.a << "}"; }
};
int main() {
    std::ostream_iterator<X> out(std::cout << std::unitbuf, " ");
    std::vector<X> vec { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    boost::intrusive::list<X> list(vec.begin(), vec.end());
    std::cout << "before: "; std::copy(list.begin(), list.end(), out);
    list.remove_if([](X const& x) { return 0 == (x.a % 2); });
    std::cout << "nafter: "; std::copy(list.begin(), list.end(), out);
}

打印

before: {1} {2} {3} {4} {5} {6} {7} {8} {9} {10} 
after: {1} {3} {5} {7} {9}

使用auto_unlink：

struct X : public bi::list_base_hook<bi::link_mode<bi::auto_unlink> > {

注意，您需要禁用list<> 的恒定时间size()（请参阅参考）

将其安装到位，甚至添加

vec.erase(vec.begin()+4);

将正确地将相应节点与侵入列表联系起来：

活在coliru 

#include <iostream>
#include <iterator>
#include <vector>
#include <boost/intrusive/list.hpp>
namespace bi = boost::intrusive;
struct X : public bi::list_base_hook<bi::link_mode<bi::auto_unlink> > {
    X(int a_in) : a{a_in} {}
    int a;
    friend std::ostream& operator<<(std::ostream& os, X const& x) { return os << "{" << x.a << "}"; }
};
int main() {
    std::ostream_iterator<X> out(std::cout << std::unitbuf, " ");
    std::vector<X> vec { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    bi::list<X, bi::constant_time_size<false> > list(vec.begin(), vec.end());
    std::cout << "before: "; std::copy(list.begin(), list.end(), out);
    list.remove_if([](X const& x) { return 0 == (x.a % 2); });
    std::cout << "nafter: "; std::copy(list.begin(), list.end(), out);
    vec.erase(vec.begin()+4);
    std::cout << "nauto-unlinked: "; std::copy(list.begin(), list.end(), out);
}

打印

before: {1} {2} {3} {4} {5} {6} {7} {8} {9} {10} 
after: {1} {3} {5} {7} {9} 
auto-unlinked: {1} {3} {6} {8} {10}
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