用随机数创建一个向量

您可以进行函数调用迭代器并将其传递到向量范围构造函数:

#include <boost/iterator/iterator_facade.hpp>
#include <iostream>
#include <vector>
#include <random>
#include <tuple>

template<class F, class Tag = std::input_iterator_tag>
class FunctionCallIterator
    : public boost::iterator_facade<
          FunctionCallIterator<F, Tag>,
          typename std::result_of<F()>::type,
          Tag,
          typename std::result_of<F()>::type
      >
{
    std::tuple<F, ptrdiff_t> m_; // Enable empty base class optimization for empty F.
    friend class boost::iterator_core_access;
    typename std::result_of<F()>::type dereference() const { return std::get<0>(m_)(); }
    bool equal(FunctionCallIterator const& b) const { return std::get<1>(m_) == std::get<1>(b.m_); }
    void increment() { ++std::get<1>(m_); }
    void decrement() { --std::get<1>(m_); }
    void advance(ptrdiff_t n) { std::get<1>(m_) += n; }
    ptrdiff_t distance_to(FunctionCallIterator const& b) const { return std::get<1>(b.m_) - std::get<1>(m_); }
public:
    FunctionCallIterator(F const& f, ptrdiff_t n) : m_(f, n) {}
};

int main() {
    std::mt19937 rng {std::random_device{}()};
    std::uniform_int_distribution<int> dist {1, 52};
    auto f = [&]{return dist(rng);};
    using RngIter = FunctionCallIterator<decltype(f), std::random_access_iterator_tag>;
    std::vector<int> vec(RngIter{f, 0}, RngIter{f, 10});
    for(auto v : vec)
        std::cout << v << '\n';
}

push_back / back_inserter

从我发现的 reserve 具有 back_inserter 应该做到:

std::mt19937 rng {std::random_device{}()};
std::uniform_int_distribution<int> dist {1, 52};

std::vector<int> vec;
const size_t size = 1000;
vec.reserve(size);
std::generate_n(std::back_inserter(vec), size, [&]{return dist(rng);} );

这似乎非常有效,但仍有容量检查,不需要: https://godbolt.org/z/sOBlLx

不确定是否 std::vector 让任何事情都比这更有效率。需要的是 uninitialized_resize

编辑:也可以在 Is this correct way to combine std::generate_n and std::back_inserter?