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std:: erase_if (std::map)

From cppreference.net

C++
Containers library
std::map
Member functions
Non-member functions
(C++20)
erase_if (std::map)
(C++20)

(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
定义于头文件 <map>
template < class Key, class T, class Compare, class Alloc,

class Pred >
std:: map < Key, T, Compare, Alloc > :: size_type
erase_if ( std:: map < Key, T, Compare, Alloc > & c,

Pred pred ) ;
(C++20 起)
(C++26 起为 constexpr)

从 c 中删除所有满足谓词 pred 的元素。

相当于 

auto old_size = c.size();
for (auto first = c.begin(), last = c.end(); first != last;)
{
    if (pred(*first))
        first = c.erase(first);
    else
        ++first;
}
return old_size - c.size();

目录

参数

c - 要从中擦除元素的容器
pred - 谓词，当应擦除元素时返回 true

返回值

被擦除的元素数量。

复杂度

线性。

示例

运行此代码 
#include <iostream>
#include <map>
void println(auto rem, const auto& container)
{
    std::cout << rem << '{';
    for (char sep[]{0, ' ', 0}; const auto& [key, value] : container)
        std::cout << sep << '{' << key << ", " << value << '}', *sep = ',';
    std::cout << "}\n";
}
int main()
{
    std::map<int, char> data
    {
        {1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'},
        {5, 'e'}, {4, 'f'}, {5, 'g'}, {5, 'g'},
    };
    println("Original:\n", data);
    const auto count = std::erase_if(data, [](const auto& item)
    {
        const auto& [key, value] = item;
        return (key & 1) == 1;
    });
    println("Erase items with odd keys:\n", data);
    std::cout << count << " items removed.\n";
}

输出： 

Original:
{{1, a}, {2, b}, {3, c}, {4, d}, {5, e}}
Erase items with odd keys:
{{2, b}, {4, d}}
3 items removed.

参见

移除满足特定条件的元素
(函数模板)
(C++20) (C++20)
移除满足特定条件的元素
(算法函数对象)