std::ranges:: remove_copy, std::ranges:: remove_copy_if, std::ranges:: remove_copy_result, std::ranges:: remove_copy_if_result

From cppreference.net

定义于头文件 `<algorithm>`
调用签名
	(1)
template < std:: input_iterator I, std:: sentinel_for < I > S, std:: weakly_incrementable O, class T, class Proj = std:: identity > requires std:: indirectly_copyable < I, O > && std:: indirect_binary_predicate < ranges:: equal_to , std :: projected < I, Proj > , const T * > constexpr remove_copy_result < I, O > remove_copy ( I first, S last, O result, const T & value, Proj proj = { } ) ;			(C++20 起) (C++26 前)
template < std:: input_iterator I, std:: sentinel_for < I > S, std:: weakly_incrementable O, class Proj = std:: identity , class T = std :: projected_value_t < I, Proj > > requires std:: indirectly_copyable < I, O > && std:: indirect_binary_predicate < ranges:: equal_to , std :: projected < I, Proj > , const T * > constexpr remove_copy_result < I, O > remove_copy ( I first, S last, O result, const T & value, Proj proj = { } ) ;			(C++26 起)
		(2)
template < ranges:: input_range R, std:: weakly_incrementable O, class T, class Proj = std:: identity > requires std:: indirectly_copyable < ranges:: iterator_t < R > , O > && std:: indirect_binary_predicate < ranges:: equal_to , std :: projected < ranges:: iterator_t < R > , Proj > , const T * > constexpr remove_copy_result < ranges:: borrowed_iterator_t < R > , O > remove_copy ( R && r, O result, const T & value, Proj proj = { } ) ;				(C++20 起) (C++26 前)
template < ranges:: input_range R, std:: weakly_incrementable O, class Proj = std:: identity , class T = std :: projected_value_t < ranges:: iterator_t < R > , Proj > > requires std:: indirectly_copyable < ranges:: iterator_t < R > , O > && std:: indirect_binary_predicate < ranges:: equal_to , std :: projected < ranges:: iterator_t < R > , Proj > , const T * > constexpr remove_copy_result < ranges:: borrowed_iterator_t < R > , O > remove_copy ( R && r, O result, const T & value, Proj proj = { } ) ;				(C++26 起)
template < std:: input_iterator I, std:: sentinel_for < I > S, std:: weakly_incrementable O, class Proj = std:: identity </a

从源范围 [ first , last ) 复制元素到以 result 开始的目标范围，跳过（经 proj 投影后）满足特定条件的元素。若源范围与目标范围重叠则行为未定义。

1) 忽略所有等于 value 的元素。

3) 忽略所有谓词 pred 返回 true 的元素。

2,4) 与 (1,3) 相同，但使用 r 作为源范围，如同以 ranges:: begin ( r ) 作为 first ，并以 ranges:: end ( r ) 作为 last 。

本页面描述的函数式实体是 算法函数对象 （非正式称为 niebloids ），即：

在调用其中任何一个函数时，都不能显式指定模板参数列表。
它们对实参依赖查找不可见。
当通过常规非限定查找将其中任何一个函数作为函数调用运算符左侧的名称找到时，会抑制实参依赖查找。

struct remove_copy_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S,
             std::weakly_incrementable O, class Proj = std::identity,
             class T = std::projected_value_t<I, Proj>>
    requires std::indirectly_copyable<I, O> &&
             std::indirect_binary_predicate<ranges::equal_to,
                                            std::projected<I, Proj>, const T*>
    constexpr ranges::remove_copy_result<I, O>
        operator()(I first, S last, O result, const T& value, Proj proj = {}) const
    {
        for (; !(first == last); ++first)
            if (value != std::invoke(proj, *first))
            {
                *result = *first;
                ++result;
            }
        return {std::move(first), std::move(result)};
    }
    template<ranges::input_range R, 
             std::weakly_incrementable O, class Proj = std::identity,
             class T = std::projected_value_t<ranges::iterator_t<R>, Proj>>
    requires std::indirectly_copyable<ranges::iterator_t<R>, O> &&
             std::indirect_binary_predicate<ranges::equal_to,
             std::projected<ranges::iterator_t<R>, Proj>, const T*>
    constexpr ranges::remove_copy_result<ranges::borrowed_iterator_t<R>, O>
        operator()(R&& r, O result, const T& value, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::move(result), value,
                       std::move(proj));
    }
};
inline constexpr remove_copy_fn remove_copy {};

remove_copy_if (3,4)

struct remove_copy_if_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O,
             class Proj = std::identity,
             std::indirect_unary_predicate<std::projected<I, Proj>> Pred>
    requires std::indirectly_copyable<I, O>
    constexpr ranges::remove_copy_if_result<I, O>
        operator()(I first, S last, O result, Pred pred, Proj proj = {}) const
    {
        for (; first != last; ++first)
            if (false == std::invoke(pred, std::invoke(proj, *first)))
            {
                *result = *first;
                ++result;
            }
        return {std::move(first), std::move(result)};
    }
    template<ranges::input_range R, std::weakly_incrementable O,
             class Proj = std::identity,
             std::indirect_unary_predicate<
                 std::projected<<a

示例

运行此代码

#include <algorithm>
#include <array>
#include <complex>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string_view>
#include <vector>
void println(const auto rem, const auto& v)
{
    std::cout << rem << ' ';
    for (const auto& e : v)
        std::cout << e << ' ';
    std::cout << '\n';
}
int main()
{
    // 从给定字符串中过滤掉井号
    const std::string_view str{"#Small #Buffer #Optimization"};
    std::cout << "处理前: " << std::quoted(str) << '\n';
    std::cout << "处理后:  \"";
    std::ranges::remove_copy(str.begin(), str.end(),
                             std::ostream_iterator<char>(std::cout), '#');
    std::cout << "\"\n";
    // 仅复制具有正虚部的复数
    using Ci = std::complex<int>;
    constexpr std::array<Ci, 5> source
    {
        Ci{1, 0}, Ci{0, 1}, Ci{2, -1}, Ci{3, 2}, Ci{4, -3}
    };
    std::vector<std::complex<int>> target;
    std::ranges::remove_copy_if
    (
        source,
        std::back_inserter(target),
        [](int imag) { return imag <= 0; },
        [](Ci z) { return z.imag(); }
    );
    println("源数组:", source);
    println("目标数组:", target);
    std::vector<std::complex<float>> nums{{2, 2}, {1, 3}, {4, 8}, {1, 3}};
    std::vector<std::complex<double>> outs;
    #ifdef __cpp_lib_algorithm_default_value_type
        std::remove_copy(nums.cbegin(), nums.cend(), std::back_inserter(outs),
                         {1, 3}); // T 被推导为 std::complex<float>
    #else
        std::remove_copy(nums.cbegin(), nums.cend(), std::back_inserter(outs),
                         std::complex<float>{1, 3});
    #endif
    println("nums:  ", nums);
    println("outs:  ", outs);
}

输出：

处理前: "#Small #Buffer #Optimization"
处理后:  "Small Buffer Optimization"
源数组: (1,0) (0,1) (2,-1) (3,2) (4,-3)
目标数组: (0,1) (3,2)
nums:   (2,2) (1,3) (4,8) (1,3)
outs:   (2,2) (4,8)

参见

ranges::remove ranges::remove_if (C++20) (C++20)	移除满足特定条件的元素 (算法函数对象)
ranges::copy ranges::copy_if (C++20) (C++20)	将元素范围复制到新位置 (算法函数对象)
ranges::copy_n (C++20)	将指定数量的元素复制到新位置 (算法函数对象)
ranges::copy_backward (C++20)	以逆序复制元素范围 (算法函数对象)
ranges::replace_copy ranges::replace_copy_if (C++20) (C++20)	复制范围，并将满足特定条件的元素替换为其他值 (算法函数对象)
ranges::reverse_copy (C++20)	创建反转后的范围副本 (算法函数对象)
ranges::rotate_copy (C++20)	复制并旋转元素范围 (算法函数对象)
ranges::unique_copy (C++20)	创建不包含连续重复元素的范围副本 (算法函数对象)
remove_copy remove_copy_if	复制元素范围，忽略满足特定条件的元素 (函数模板)

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Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Diagnostics library
Memory management library
Metaprogramming library (C++11)
General utilities library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Technical specifications
Symbols index
External libraries

first, last	-	定义待处理元素源范围的迭代器-哨位对
r	-	元素的源范围
result	-	目标范围的起始位置
value	-	不被复制元素的值
comp	-	用于比较投影元素的二元谓词
proj	-	应用于元素的投影

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Variants

std::ranges:: remove_copy, std::ranges:: remove_copy_if, std::ranges:: remove_copy_result, std::ranges:: remove_copy_if_result

目录

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可能的实现

示例

参见