std::ranges::search

#include <algorithm>
#include <cctype>
#include <iostream>
#include <iterator>
#include <string_view>
using namespace std::literals;
void print(int id, const auto& haystack, const auto& needle, const auto& found)
{
    std::cout << id << ") search(\"" << haystack << "\", \"" << needle << "\"); ";
    const auto first = std::distance(haystack.begin(), found.begin());
    const auto last = std::distance(haystack.begin(), found.end());
    if (found.empty())
        std::cout << "not found;";
    else
    {
        std::cout << "found: \"";
        for (const auto x : found)
            std::cout << x;
        std::cout << "\";";
    }
    std::cout << " subrange: {" << first << ", " << last << "}\n";
}
int main()
{
    constexpr auto haystack {"abcd abcd"sv};
    constexpr auto needle {"bcd"sv};
    // 使用迭代器对 begin()/end() 进行搜索：
    constexpr auto found1 = std::ranges::search(
        haystack.begin(), haystack.end(),
        needle.begin(), needle.end());
    print(1, haystack, needle, found1);
    // 使用范围 r1, r2 进行搜索：
    constexpr auto found2 = std::ranges::search(haystack, needle);
    print(2, haystack, needle, found2);
    // 'needle' 范围为空：
    constexpr auto none {""sv};
    constexpr auto found3 = std::ranges::search(haystack, none);
    print(3, haystack, none, found3);
    // 'needle' 将不会被找到：
    constexpr auto awl {"efg"sv};
    constexpr auto found4 = std::ranges::search(haystack, awl);
    print(4, haystack, awl, found4);
    // 使用自定义比较器和投影进行搜索：
    constexpr auto bodkin {"234"sv};
    auto found5 = std::ranges::search(haystack, bodkin,
        [](const int x, const int y) { return x == y; }, // pred
        [](const int x) { return std::toupper(x); }, // proj1
        [](const int y) { return y + 'A' - '1'; }); // proj2
    print(5, haystack, bodkin, found5);
}