std::set_difference - cppreference.com (original) (raw)

Copies the elements from the sorted range [first1, last1) which are not found in the sorted range [first2, last2) to the range beginning at d_first. The output range is also sorted.

If [first1, last1) contains m elements that are equivalent to each other and [first2, last2) contains n elements that are equivalent to them, the final std::max(m - n, 0) elements will be copied from [first1, last1) to the output range, preserving order.

1. If [first1, last1) or [first2, last2) is not sorted with respect to operator<(until C++20)std::less{}(since C++20), the behavior is undefined.

2. If [first1, last1) or [first2, last2) is not sorted with respect to comp, the behavior is undefined.

2,4) Same as (1,3), but executed according to policy.

These overloads participate in overload resolution only if all following conditions are satisfied:

If the output range overlaps with [first1, last1) or [first2, last2), the behavior is undefined.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Exceptions
• 5 Possible implementation
• 6 Example
• 7 Defect reports
• 8 See also

[edit] Parameters

[edit] Return value

Iterator past the end of the constructed range.

[edit] Complexity

Given \(\scriptsize N_1\)N1 as std::distance(first1, last1) and \(\scriptsize N_2\)N2 as std::distance(first2, last2):

1,2) At most \(\scriptsize 2 \cdot (N_1+N_2)-1\)2⋅(N1+N2)-1 comparisons using operator<(until C++20)std::less{}(since C++20).

3,4) At most \(\scriptsize 2 \cdot (N_1+N_2)-1\)2⋅(N1+N2)-1 applications of the comparison function comp.

[edit] 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 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.

[edit] Possible implementation

[edit] Example

#include #include #include #include   template std::ostream& operator<<(std::ostream& os, const std::vector& v) { os << '{'; for (auto n{v.size()}; const auto& e : v) os << e << (--n ? ", " : ""); return os << '}'; }   struct Order // a struct with very interesting data { int order_id{};   friend std::ostream& operator<<(std::ostream& os, const Order& ord) { return os << ord.order_id; } };   int main() { const std::vector v1{1, 2, 5, 5, 5, 9}; const std::vector v2{2, 5, 7}; std::vector diff;   std::set_difference(v1.begin(), v1.end(), v2.begin(), v2.end(), std::inserter(diff, diff.begin()));   std::cout << v1 << " ∖ " << v2 << " == " << diff << "\n\n";   // we want to know which orders "cut" between old and new states: std::vector old_orders{{1}, {2}, {5}, {9}}; std::vector new_orders{{2}, {5}, {7}}; std::vector cut_orders;   std::set_difference(old_orders.begin(), old_orders.end(), new_orders.begin(), new_orders.end(), std::back_inserter(cut_orders), [](auto& a, auto& b) { return a.order_id < b.order_id; });   std::cout << "old orders: " << old_orders << '\n' << "new orders: " << new_orders << '\n' << "cut orders: " << cut_orders << '\n'; }

Output:

{1, 2, 5, 5, 5, 9} ∖ {2, 5, 7} == {1, 5, 5, 9}   old orders: {1, 2, 5, 9} new orders: {2, 5, 7} cut orders: {1, 9}

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also