实现C ++ 14 make_integer_sequence

本文介绍了实现C ++ 14 make_integer_sequence的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 我尝试实施 C ++ 14 别名模板 make_integer_sequence ，它简化了类模板的创建 integer_sequence 。I tried to implement the C++14 alias template make_integer_sequence, which simplifies the creation of the class template integer_sequence.template< class T, T... I> struct integer_sequence{ typedef T value_type; static constexpr size_t size() noexcept { return sizeof...(I) ; }};template< class T, T N>using make_integer_sequence = integer_sequence< T, 0,1,2, ... ,N-1 >; // only for illustration.要实现 make_integer_sequence ，我们需要一个辅助结构 make_helper 。To implement make_integer_sequence we need a helper structure make_helper.template< class T , class N >using make_integer_sequence = typename make_helper<T,N>::type;实现 make_helpertemplate< class T, T N, T... I >struct make_helper{ typedef typename mpl::if_< T(0) == N, mpl::identity< integer_sequence<T,I...> >, make_helper< T, N-1, N-1,I...> >::type;};要测试 make_integer_sequence ：int main(){ #define GEN(z,n,temp) \ typedef make_integer_sequence< int, n > BOOST_PP_CAT(int_seq,n) ; BOOST_PP_REPEAT(256, GEN, ~);}我使用GCC 4.8.0编译程序，在四核i5系统具有8GB的RAM。 成功编译需要4秒。I compiled the program with GCC 4.8.0, on a quad-core i5 system with 8GBs of RAM.Successful compilation took 4 seconds.但是，当我将GEN宏更改为：But, when I changed the GEN macro to:int main() {#define GEN(z,n,temp) \typedef make_integer_sequence< int, n * 4 > BOOST_PP_CAT(int_seq, n) ;BOOST_PP_REPEAT(256, GEN, ~ );}编译失败并输出错误信息：The compilation was unsuccessful and outputted the error message: 虚拟内存耗尽。 virtual memory exhausted.有人可以解释这个错误，导致了？Could somebody explain this error and what caused it?编辑：我将测试简化为：int main(){ typedef make_integer_sequence< int, 4096 > int_seq4096;}然后我成功编译了GCC 4.8.0 -ftemplate-depth = 65536。I then successfully compiled with GCC 4.8.0 -ftemplate-depth=65536.但是第二个测试：int main(){ typedef make_integer_sequence< int, 16384 > int_seq16384;}未使用GCC 4.8.0 -ftemplate-depth = 65536编译，导致错误：Did not compile with GCC 4.8.0 -ftemplate-depth=65536, and resulted in the error: 虚拟内存耗尽。 virtual memory exhausted.所以，我的问题是，如何减少模板深度实例化？So, my question is, how do I decrease template deep instantiation?尊敬的， Khurshid。Regards,Khurshid.推荐答案这里是 log N 实现，甚至不需要增加模板实例的最大深度和编译速度相当快：Here's a log N implementation that doesn't even need an increased max-depth for template instantiations and compiles pretty fast:// using aliases for cleaner syntaxtemplate<class T> using Invoke = typename T::type;template<unsigned...> struct seq{ using type = seq; };template<class S1, class S2> struct concat;template<unsigned... I1, unsigned... I2>struct concat<seq<I1...>, seq<I2...>> : seq<I1..., (sizeof...(I1)+I2)...>{};template<class S1, class S2>using Concat = Invoke<concat<S1, S2>>;template<unsigned N> struct gen_seq;template<unsigned N> using GenSeq = Invoke<gen_seq<N>>;template<unsigned N>struct gen_seq : Concat<GenSeq<N/2>, GenSeq<N - N/2>>{};template<> struct gen_seq<0> : seq<>{};template<> struct gen_seq<1> : seq<0>{}; 这篇关于实现C ++ 14 make_integer_sequence的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！