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# std::includes

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class InputIt1, class InputIt2 > bool includes( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2 ); | (1) |
template< class InputIt1, class InputIt2 > bool includes( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Compare comp ); | (2) |

Returns true if every element from the sorted range `[first2, last2)` is found within the sorted range `[first1, last1)`. Also returns true if `[first2, last2)` is empty.

The first version expects both ranges to be sorted with operator<, the second version expects them to be sorted with the given comparison function `comp`.

### [edit] Parameters

first1, last1 | - | the sorted range of elements to examine
first2, last2 | - | the sorted range of elements to search for
comp | - | comparison function object (i.e. an object that satisfies the requirements of `Compare`) which returns ​true if the first argument is less than (i.e. is ordered before) the second. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1 &a, const Type2 &b); The signature does not need to have const &, but the function object must not modify the objects passed to it. The types Type1 and Type2 must be such that an object of type InputIt can be dereferenced and then implicitly converted to both of them. ​
Type requirements
- `InputIt` must meet the requirements of `InputIterator`.

### [edit] Return value

true if every element from `[first2, last2)` is a member of `[first, last)`.

### [edit] Complexity

At most 2·(N1+N2-1) comparisons, where N1 = std::distance(first1, last1) and N2 = std::distance(first2, last2).

### [edit] Possible implementation

First version
    template<class InputIt1, class InputIt2>
    bool includes(InputIt1 first1, InputIt1 last1,
                  InputIt2 first2, InputIt2 last2)
    {
        for (; first2 != last2; ++first1)
        {
            if (first1 == last1 || *first2 < *first1)
                return false;
            if ( !(*first1 < *first2) )
                ++first2;
        }
        return true;
    }
Second version
    template<class InputIt1, class InputIt2>
    bool includes(InputIt1 first1, InputIt1 last1,
                  InputIt2 first2, InputIt2 last2, Compare comp)
    {
        for (; first2 != last2; ++first1)
        {
            if (first1 == last1 || comp(*first2, *first1))
                return false;
            if (!comp(*first1, *first2))
                ++first2;
        }
        return true;
    }

### [edit] Example

Run this code

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

    int main()
    {
      std::vector<char> v1 {'a', 'b', 'c', 'f', 'h', 'x'};
      std::vector<char> v2 {'a', 'b', 'c'};
      std::vector<char> v3 {'a', 'c'};
      std::vector<char> v4 {'g'};
      std::vector<char> v5 {'a', 'c', 'g'};
      std::vector<char> v6;

      for (auto i : v1) std::cout << i << ' ';
      std::cout << "includes:\n";

      for (auto i : v2) std::cout << i << ' ';
      std::cout << ": " << std::includes(v1.begin(), v1.end(), v2.begin(), v2.end()) << '\n';
      for (auto i : v3) std::cout << i << ' ';
      std::cout << ": " << std::includes(v1.begin(), v1.end(), v3.begin(), v3.end()) << '\n';
      for (auto i : v4) std::cout << i << ' ';
      std::cout << ": " << std::includes(v1.begin(), v1.end(), v4.begin(), v4.end()) << '\n';
      for (auto i : v5) std::cout << i << ' ';
      std::cout << ": " << std::includes(v1.begin(), v1.end(), v5.begin(), v5.end()) << '\n';
      for (auto i : v6) std::cout << i << ' ';
      std::cout << ": " << std::includes(v1.begin(), v1.end(), v6.begin(), v6.end()) << '\n';

      auto cmp_nocase = [](char a, char b) {
        return std::tolower(a) < std::tolower(b);
      };
      std::vector<char> v7 {'A', 'B', 'C'};
      for (auto i : v7) std::cout << i << ' ';
      std::cout << ": "
                << std::includes(v1.begin(), v1.end(), v7.begin(), v7.end(), cmp_nocase)
                << '\n';
    }

Output:

    a b c f h x includes:
    a b c : 1
    a c : 1
    g : 0
    a c g : 0
    A B C : 1

### [edit] See also

set_difference | computes the difference between two sets (function template) [edit]
search | searches for a range of elements (function template) [edit]

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