Why does the program display 0? The function description says Returns true if the sorted range [first1, last1) contains all the elements in the sorted range [first2, last2). http://www.cplusplus.com/reference/algorithm/includes/ . But a contains all elements from b (1 and 2)
std::vector a{1, 2}; std::vector b{1, 2, 1, 2}; std::cout << std::includes(a.begin(), a.end(), b.begin(), b.end()); 
std::vector<int> a{1, 2}; // тут вы забыли аргумент шаблона std::vector<int> b{1, 2, 1, 2}; Swap the objects and it will work.
std::swap(a, b); std::cout << std::includes(a.begin(), a.end(), b.begin(), b.end()); if b is a subset of a , then get a positive result
b{2,2,1,1} - it may not work out :) - HarryHere, in essence, it is checked whether the range is completely in another range, and the set difference is not calculated. Therefore, the same elements are quite permissible (as in a multiset), and the range a clearly not enough to include the range b .
But on the contrary - quite: check for yourself
std::cout << std::includes(b.begin(), b.end(), a.begin(), a.end()); but don't forget to sort :)
In other words, a is a subset of b , but b not a subset of a - if only because it has more elements :)
Source: https://ru.stackoverflow.com/questions/921770/
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sorted rangerequirement is clearly not met. - VTT