# std::includes

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class InputIt1, class InputIt2 > bool includes( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2 ); | (1) |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > bool includes( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2 ); | (2) | (since C++17)
template< class InputIt1, class InputIt2, class Compare > bool includes( InputIt1 first1, InputIt1 last1, InputIt2 first2, InputIt2 last2, Compare comp ); | (3) |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class Compare > bool includes( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2, ForwardIt2 last2, Compare comp ); | (4) | (since C++17)

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.

1) Both ranges must be sorted with operator<.
3) Both ranges must be sorted with the given comparison function `comp`.
2,4) Same as (1,3), but executed according to `policy`. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

### Parameters

first1, last1 | - | the sorted range of elements to examine
first2, last2 | - | the sorted range of elements to search for
policy | - | the execution policy to use. See execution policy for details.

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
- `InputIt1, InputIt2` must meet the requirements of `InputIterator`.
- `ForwardIt1, ForwardIt2` must meet the requirements of `ForwardIterator`.

### Return value

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

### Complexity

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

### Exceptions

The overloads with a template parameter named `ExecutionPolicy` report errors as follows:

- If execution of a function invoked as part of the algorithm throws an exception and `ExecutionPolicy` is one of the three standard policies, std::terminate is called. For any other `ExecutionPolicy`, the behavior is implementation-defined.
- If the algorithm fails to allocate memory, std::bad_alloc is thrown.

### 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;
    }

### 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'};

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

      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';

      auto cmp_nocase = [](char a, char b) {
        return std::tolower(a) < std::tolower(b);
      };

      std::vector<char> v6 {'A', 'B', 'C'};
      for (auto i : v6) std::cout << i << ' ';
      std::cout << ": (case-insensitive) "
                << std::includes(v1.begin(), v1.end(), v6.begin(), v6.end(), cmp_nocase)
                << '\n';
    }

Output:

    a b c f h x
    includes:
    a b c : true
    a c : true
    g : false
    a c g : false
    A B C : (case-insensitive) true

### See also

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

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