Difference between std::search and std::find_first_of

问题

I am trying to grasp the difference between std::search and std::find_first_of

They have the same prototypes:

template <class ForwardIterator1, class ForwardIterator2>
   ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1,
                                   ForwardIterator2 first2, ForwardIterator2 last2);

template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
   ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1,
                                   ForwardIterator2 first2, ForwardIterator2 last2,
                                   BinaryPredicate pred);

template <class ForwardIterator1, class ForwardIterator2>
   ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1,
                            ForwardIterator2 first2, ForwardIterator2 last2);

template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
   ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1,
                            ForwardIterator2 first2, ForwardIterator2 last2,
                            BinaryPredicate pred);

They both return the same thing: An iterator to the first occurrence of the sequence [first2, last2) inside [first1, last1). (using equality, or a binary predicate)

So what is the difference ? Am I wrong ?

回答1:

The difference is that std::search searches for a whole range of elements within another range, while std::find_first_of searches for a single element from a range within another range.

回答2:

std::find_first_of is looking for any of the elements in your search range. It will return an iterator to the first occurrence of any of the elements in [s_first1, s_first2].

std::search is looking for the whole sequence you passed. Such, it will return an iterator to the first occurrence of the sequence [s_first1, s_first2].

#include <vector>
#include <iostream>
#include <algorithm>

int main() {
    std::vector<int> A{1, 2, 3, 2, 4, 6, 5};
    std::vector<int> search_range{2, 4, 6};
    std::vector<int> find_first_of_range{6, 5};

    auto it_search = std::search(A.begin(), A.end(),
        search_range.begin(), search_range.end());
    std::cout << std::distance(A.begin(), it_search) << std::endl; // 3

    auto it_find_first_of = std::find_first_of(A.begin(), A.end(),
        find_first_of_range.begin(), find_first_of_range.end());
    std::cout << std::distance(A.begin(), it_find_first_of) << std::endl; // 5
}

Runnable on Coliru.

回答3:

std::search() finds where the range of elements that matches the entire sequence of [first2..last2) is, while find_first_of() finds the first single element that matches one of the elements in [first2..last2).

来源：https://stackoverflow.com/questions/21017338/difference-between-stdsearch-and-stdfind-first-of

标签

c++

find

std