constexpr /*iterator*/ begin();
(since C++20)

Returns an iterator to the first found subrange.

In order to provide the amortized constant time complexity required by the range concept, this function caches the result within the split_view for use on subsequent calls. Equivalent to.

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

Exposition only data members base_ and cached_begin_ are described here.



Return value

An iterator.


Amortized \(\scriptsize \mathcal{O}(1)\)O(1).


A link to check the code: wandbox.

#include <iostream>
#include <iomanip>
#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 (std::string_view word: words)
        std::cout << std::quoted(word) << ' ';
    std::ranges::split_view letters{ sentence, std::string_view{""} };
    std::cout << "\nbegin(): " << std::quoted( std::string_view{*letters.begin()} )
              << "\nLetters: ";
    for (std::string_view letter: letters)
        std::cout << std::quoted(letter, '\'') << ' ';


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' '.' '.'

See also

returns an iterator or a sentinel to the end
(public member function)
returns an iterator to the beginning
(public member function of std::ranges::lazy_split_view<V,Pattern>)
returns an iterator to the beginning of a range
(customization point object)

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