容器库(5)-std::list

std::forward_list是可以从任何位置快速插入和移除元素的容器，不支持快速随机访问，支持正向和反向的迭代。

本文章的代码库：

https://gitee.com/gamestorm577/CppStd

成员函数

构造、析构和赋值

构造函数

可以用元素、元素列表、迭代器或者另一个list来构造list。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::vector vec{1.1f, 2.1f, 3.1f};
std::list l1(5, 1.1f);
std::list l2(5);
std::list l3(vec.begin(), vec.end());
std::list l4(l1);
std::list tmp(l1);
std::list l5(std::move(tmp));
std::list l6{11.1f, 12.1, 13.1f};

print_func(l1);
print_func(l2);
print_func(l3);
print_func(l4);
print_func(l5);
print_func(l6);

输出结果：

1.1 1.1 1.1 1.1 1.1 
0 0 0 0 0 
1.1 2.1 3.1 
1.1 1.1 1.1 1.1 1.1 
1.1 1.1 1.1 1.1 1.1 
11.1 12.1 13.1 

析构函数

list析构时，会按照正向顺序依次删除元素。代码示例：

struct MyStruct
{
    MyStruct(int i)
        : Index(i)
    {
    }

    ~MyStruct()
    {
        std::cout << "destruct, Index = " << Index << std::endl;
    }

    int Index = 0;
};

std::list l;
l.emplace_front(1);
l.emplace_front(3);
l.emplace_front(5);

输出结果：

destruct, Index = 5
destruct, Index = 3
destruct, Index = 1

赋值函数

可以用元素列表或者另一个list赋值给forward_list。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list tmp = {1.1f, 2.1f, 3.1f};
std::list l1;
std::list l2;

l1 = tmp;
l2 = {2.1f, 2.2f, 2.3f, 2.4f};
print_func(l1);
print_func(l2);

输出结果：

1.1 2.1 3.1 
2.1 2.2 2.3 2.4 

assign

将值赋值给forward_list，可以是元素、元素列表或者迭代器。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::vector vec(10, 1.2f);
std::list l;

l.assign(5, 1.2);
print_func(l);
l.assign(vec.begin(), vec.end());
print_func(l);
l.assign({1.1f, 2.1f, 3.1f});
print_func(l);

输出结果：

1.2 1.2 1.2 1.2 1.2 
1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 
1.1 2.1 3.1 

元素访问

front

返回首个元素的引用。示例代码：

std::list l = {1.f, 2.f, 3.f};
l.front() = 4.1f;
std::cout << "l front is: " << l.front() << std::endl;

输出结果：

l front is: 4.1

back

返回最后一个元素的引用。示例代码：

std::list l = {1.f, 2.f, 3.f};
l.back() = 24.1f;
std::cout << "l back is: " << l.back() << std::endl;

输出结果：

l back is: 24.1

迭代器

接口begin、cbegin指向list起始的迭代器，end、cend指向末尾的迭代器。rbegin、crbegin指向起始的逆向迭代器，rend、crend指向末尾的逆向迭代器。代码示例：

std::list l = {1.1f, 2.1f, 3.1f};
for (auto iter = l.rbegin(); iter != l.rend(); ++iter)
{
    *iter += 27.f;
}

for (auto iter = l.crbegin(); iter != l.crend(); ++iter)
{
    std::cout << "num is: " << *iter << std::endl;
}

输出结果：

num is: 30.1
num is: 29.1
num is: 28.1

容量

empty

检查list是否为空。示例代码：

std::list l1 = {1.1f, 2.1f, 3.1f};
std::list l2;
std::cout << std::boolalpha;
std::cout << "l1 empty: " << l1.empty() << std::endl;
std::cout << "l2 empty: " << l2.empty() << std::endl;

输出结果：

l1 empty: false
l2 empty: true

size

获取list元素的个数。代码示例：

std::list l1 = {1.1f, 2.1f, 3.1f};
std::list l2;
std::cout << "l1 size = " << l1.size() << std::endl;
std::cout << "l2 size = " << l2.size() << std::endl;

输出结果：

l1 size = 3
l2 size = 0

max_size

返回可以容纳的最大元素个数。代码示例：

struct MyStruct
{
    double num1;
    double num2;
    double num3;
    double num4;
};

std::list l1;
std::list l2;
std::list l3;
std::cout << "l1 max size = " << l1.max_size() << std::endl;
std::cout << "l2 max size = " << l2.max_size() << std::endl;
std::cout << "l3 max size = " << l3.max_size() << std::endl;

输出结果：

l1 max size = 768614336404564650
l2 max size = 768614336404564650
l3 max size = 384307168202282325

修改器

clear

清除所有的元素。代码示例：

std::list l(3, 1.f);
std::cout << std::boolalpha;
std::cout << "l empty: " << l.empty() << std::endl;
l.clear();
std::cout << "l empty: " << l.empty() << std::endl;

输出结果：

l empty: false
l empty: true

insert

在指定的位置插入元素。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::vector vec{40.1f, 40.2f};

std::list l = {1.1f, 1.2f, 1.3f};
print_func(l);
l.insert(l.begin(), 15.7f);
print_func(l);
l.insert(std::next(l.begin(), 2), 3, 27.9f);
print_func(l);
l.insert(std::next(l.begin(), 1), vec.begin(), vec.end());
print_func(l);
l.insert(std::next(l.begin(), 1), {70.5f, 75.5f, 71.5f});
print_func(l);

输出结果：

1.1 1.2 1.3 
15.7 1.1 1.2 1.3 
15.7 1.1 27.9 27.9 27.9 1.2 1.3 
15.7 40.1 40.2 1.1 27.9 27.9 27.9 1.2 1.3 
15.7 70.5 75.5 71.5 40.1 40.2 1.1 27.9 27.9 27.9 1.2 1.3 

emplace

在指定位置一个元素。代码示例：

struct MyStruct
{
    MyStruct(float num1, int num2)
    {
        std::cout << "construct " << num1 << " " << num2 << std::endl;
    }
};

std::list f;
f.emplace(f.begin(), 5.5f, 20);

输出结果：

construct 5.5 20

erase

删除指定位置的元素。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list l = {1.1f, 1.2f, 1.3f, 1.5f, 1.6f, 1.7f, 1.8f};
print_func(l);
l.erase(std::next(l.begin(), 1));
print_func(l);
l.erase(std::next(l.begin(), 1), std::next(l.begin(), 5));
print_func(l);

输出结果：

1.1 1.2 1.3 1.5 1.6 1.7 1.8 
1.1 1.3 1.5 1.6 1.7 1.8 
1.1 1.8 

push_back

将元素添加到末尾。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list l = {1.1f, 1.2f};
l.push_back(1.3f);
l.push_back(1.4f);
print_func(l);

输出结果：

1.1 1.2 1.3 1.4 

emplace_back

在列表末尾构造一个元素。代码示例：

struct MyStruct
{
    MyStruct(float num1, int num2)
    {
        std::cout << "construct " << num1 << " " << num2 << std::endl;
    }
};

std::list l;
l.emplace_back(1.5f, 17);
l.emplace_back(2.3f, 4);

输出结果：

construct 1.5 17
construct 2.3 4

pop_back

移除末尾的元素。代码示例：

std::list l = {1.1f, 1.2f, 1.3f};
std::cout << "l back is: " << l.back() << std::endl;
l.pop_back();
std::cout << "l back is: " << l.back() << std::endl;

输出结果：

l back is: 1.3
l back is: 1.2

push_front

将元素添加到起始位置。代码示例：

std::list l = {1.1f, 1.2f, 1.3f};
std::cout << "l front is: " << l.front() << std::endl;
l.push_front(17.7f);
std::cout << "l front is: " << l.front() << std::endl;

输出结果：

l front is: 1.1
l front is: 17.7

emplace_front

在列表起始位置构造一个元素。代码示例：

struct MyStruct
{
    MyStruct(float num1, int num2)
    {
        std::cout << "construct " << num1 << " " << num2 << std::endl;
    }
};

std::list l;
l.emplace_front(2.7f, 17);
l.emplace_front(15.1f, 13);

输出结果：

construct 2.7 17
construct 15.1 13

pop_front

移除列表的首个元素。代码示例：

std::list l = {1.1f, 1.2f, 1.3f};
std::cout << "l front is: " << l.front() << std::endl;
l.pop_front();
std::cout << "l front is: " << l.front() << std::endl;

输出结果：

l front is: 1.1
l front is: 1.2

resize

重新设置元素的个数。代码示例：

std::list l = {1.1f, 1.2f, 1.3f};
std::cout << "l size is: " << l.size() << std::endl;
l.resize(2);
std::cout << "l size is: " << l.size() << std::endl;
l.resize(20);
std::cout << "l size is: " << l.size() << std::endl;

输出结果：

l size is: 3
l size is: 2
l size is: 20

swap

交换两个列表的元素内容。代码示例：

std::list l1 = {1.1f, 1.2f, 1.3f};
std::list l2 = {2.1f, 2.2f};
l1.swap(l2);
std::cout << "l1 size = " << l1.size() << std::endl;
std::cout << "l2 size = " << l2.size() << std::endl;

输出结果：

l1 size = 2
l2 size = 3

操作

sort

对元素进行排序。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list l = {7, 17, 5, 47, 25};
print_func(l);

l.sort();
print_func(l);

l.sort(
    [](int a, int b)
    {
        return a > b;
    });
print_func(l);

输出结果：

7 17 5 47 25 
5 7 17 25 47 
47 25 17 7 5 

merge

合并两个有序的列表。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

{
    std::list l1 = {1, 5, 7, 19};
    std::list l2 = {2, 3, 14, 15};
    l1.merge(l2);
    print_func(l1);
}

{
    std::list l1 = {1, 5, 7, 19};
    std::list l2 = {2, 3, 14, 15};
    l1.merge(l2,
             [](int a, int b)
             {
                 return a > b;
             });
    print_func(l1);
}

输出结果：

1 2 3 5 7 14 15 19 
2 3 14 15 1 5 7 19 

splice

将另一个列表中的一些元素移动到this列表指定的位置。代码示例：

auto print_func = [](std::string tag, const std::list& list)
{
    std::cout << tag;
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

{
    std::list l1 = {1.5f, 5.5f, 7.5f, 19.5f};
    std::list l2 = {2.4f, 3.4f, 14.4f, 15.4f};
    l1.splice(l1.begin(), l2);
    print_func("l1 = ", l1);
    print_func("l2 = ", l2);
}

{
    std::list l1 = {1.5f, 5.5f, 7.5f, 19.5f};
    std::list l2 = {2.4f, 3.4f, 14.4f, 15.4f};
    l1.splice(std::next(l1.begin(), 2), l2, std::next(l2.begin(), 1));
    print_func("l1 = ", l1);
    print_func("l2 = ", l2);
}

{
    std::list l1 = {1.5f, 5.5f, 7.5f, 19.5f};
    std::list l2 = {2.4f, 3.4f, 14.4f, 15.4f};
    l1.splice(l1.begin(), l2, l2.begin(), std::next(l2.begin(), 2));
    print_func("l1 = ", l1);
    print_func("l2 = ", l2);
}

输出结果：

l1 = 2.4 3.4 14.4 15.4 1.5 5.5 7.5 19.5 
l2 = 
l1 = 1.5 5.5 3.4 7.5 19.5 
l2 = 2.4 14.4 15.4 
l1 = 2.4 3.4 1.5 5.5 7.5 19.5 
l2 = 14.4 15.4 

remove、remove_if

remove移除等于指定值的元素。remove_if移除满足指定要求的元素。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list l = {5, 9, 17, 27, 15, 5, 5};
print_func(l);

l.remove(5);
print_func(l);

l.remove_if(
    [](int n)
    {
        return n > 15;
    });
print_func(l);

输出结果：

5 9 17 27 15 5 5 
9 17 27 15 
9 15 

reverse

反转元素的顺序。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list l = {1.1f, 3.1f, 19.1f, 7.1f};
print_func(l);
l.reverse();
print_func(l);

输出结果：

1.1 3.1 19.1 7.1 
7.1 19.1 3.1 1.1 

unique

删除连续的重复元素。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list l = {1, 3, 3, 17, 7, 3, 17, 17, 19, 1, 3, 1};
print_func(l);
l.unique();
print_func(l);

输出结果：

1 3 3 17 7 3 17 17 19 1 3 1 
1 3 17 7 3 17 19 1 3 1 

非成员函数

比较运算符

operator==,!=,<,<=,>,>=用于比较两个forward_list。代码示例：

std::list l1 = {1, 2, 3, 4};
std::list l2 = {1, 5};
std::cout << std::boolalpha;
std::cout << "l1 == l2: " << (l1 == l2) << std::endl;
std::cout << "l1 != l2: " << (l1 != l2) << std::endl;
std::cout << "l1 <  l2: " << (l1 < l2) << std::endl;
std::cout << "l1 <= l2: " << (l1 <= l2) << std::endl;
std::cout << "l1 >  l2: " << (l1 > l2) << std::endl;
std::cout << "l1 >= l2: " << (l1 >= l2) << std::endl;

输出结果：

l1 == l2: false
l1 != l2: true
l1 <  l2: true
l1 <= l2: true
l1 >  l2: false
l1 >= l2: false

swap

交换两个列表的元素内容。示例代码：

std::list l1 = {1.5f, 2.5f};
std::list l2 = {17.1f, 15.1f, 27.1f};
std::swap(l1, l2);
std::cout << "l1 front is: " << l1.front() << std::endl;
std::cout << "l2 front is: " << l2.front() << std::endl;

输出结果：

l1 front is: 17.1
l2 front is: 1.5

erase、erase_if

erase删除等于指定值的元素，erase_if删除满足条件的元素。代码示例：

auto print_func = [](const std::list& list)
{
    for (auto i : list)
    {
        std::cout << i << " ";
    }
    std::cout << std::endl;
};

std::list l = {5, 7, 17, 29, 7, 7, 35};
print_func(l);

std::erase(l, 7);
print_func(l);

std::erase_if(l,
              [](int a)
              {
                  return a > 17;
              });
print_func(l);

输出结果：

5 7 17 29 7 7 35 
5 17 29 35 
5 17