std::ranges::split_view<V,Pattern>:: begin

返回指向首个找到的子范围的 迭代器 。

为满足 range 概念所要求的均摊常数时间复杂度，此函数会在 split_view 内部缓存结果（通过 cached_begin_ 成员实现），供后续调用使用。

令 base_ 为底层数据成员。等价于：

constexpr /*iterator*/ begin()
{
    if (!cached_begin_.has_value())
        cached_begin_ = this->find_next(ranges::begin(base_));
    return {*this, ranges::begin(base_), cached_begin_.value()};
}

返回值

一个 迭代器 。

复杂度

均摊 \(\scriptsize \mathcal{O}(1)\) O(1) 。

示例

#include <iomanip>
#include <iostream>
#include <ranges>
#include <string_view>
int main()
{
    constexpr std::string_view sentence{"Keep..moving..forward.."};
    constexpr std::string_view delim{".."};
    std::ranges::split_view words{sentence, delim};
    std::cout << "begin(): " << std::quoted(std::string_view{*words.begin()})
              << "\nSubstrings: ";
    for (auto word : words)
        std::cout << std::quoted(std::string_view(word)) << ' ';
    std::ranges::split_view letters{sentence, std::string_view{""}};
    std::cout << "\nbegin(): " << std::quoted(std::string_view{*letters.begin()})
              << "\nLetters: ";
    for (auto letter : letters)
        std::cout << std::string_view(letter) << ' ';
    std::cout << '\n';
}

begin(): "Keep"
Substrings: "Keep" "moving" "forward" ""
begin(): "K"
Letters: K e e p . . m o v i n g . . f o r w a r d . .

参见