std::ranges::generate_n - cppreference.com (original) (raw)

| Defined in header | | | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ------------- | | Call signature | | | | template< std::input_or_output_iterator O, std::copy_constructible F > requires std::invocable<F&> && std::indirectly_writable<O, std::invoke_result_t<F&>> constexpr O generate_n( O first, std::iter_difference_t<O> n, F gen ); | | (since C++20) |

Assigns the result of successive invocations of the function object gen to each element in the range [first, first + n), if 0 < n. Does nothing otherwise.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Possible implementation
• 5 Example
• 6 See also

[edit] Parameters

[edit] Return value

Iterator one past the last element assigned if 0 < count, first otherwise.

[edit] Complexity

Exactly n invocations of gen() and assignments.

[edit] Possible implementation

[edit] Example

#include #include #include #include #include   auto dice() { static std::uniform_int_distribution distr {1, 6}; static std::random_device engine; static std::mt19937 noise {engine()}; return distr(noise); }   void print(const auto& v, std::string_view comment) { for (int i : v) std::cout << i << ' '; std::cout << '(' << comment << ")\n"; }   int main() { std::array<int, 8> v;   std::ranges::generate_n(v.begin(), v.size(), dice); print(v, "dice");   std::ranges::generate_n(v.begin(), v.size(), [n {0}] mutable { return n++; }); // same effect as std::iota(v.begin(), v.end(), 0); print(v, "iota"); }

Possible output:

5 5 2 2 6 6 3 5 (dice) 0 1 2 3 4 5 6 7 (iota)

[edit] See also