c++14

问题 Say I have a abstract base class defined like so: interface.hpp #ifndef INTERFACE_HPP #define INTERFACE_HPP 1 class interface{ public: virtual void func() = 0; }; #endif // INTERFACE_HPP Then I compile a translation unit test.cpp into a shared object test.so : test.cpp #include "interface.hpp" #include <iostream> class test_interface: public interface{ public: void func(){std::cout << "test_interface::func() called\n";} }; extern "C" interface &get_interface(){ static test_interface test;

问题 Assume there is a template function foo() which accepts an arbitrary number of arguments. Given the last argument is always an std::function , how do I implement a foo() template shown below in a way that CbArgs would contain this std::function 's parameters? template<typename... InArgs, typename... CbArgs = ???> // ^^^^^^^^^^^^ void foo(InArgs... args) { ... } For example, CbArgs should be {int,int} if invoked like this: std::function<void(int,int)> cb; foo(5, "hello", cb); My first idea was

问题 I developed some kind of meta object mechanism in a project, in order to associate type names and properties of any type to an object (see the result here). I have a dirty code working and I'm trying to make it cleaner. Given the following dummy structures: struct A { using Self = A; using Base = void; static std::string get_type_name(){ return { "A" }; } static std::vector<int> get_properties(){ return { 0 }; } }; #define SELF(class_name)\ using Base = Self;\ using Self = class_name; struct

问题 Who knows how to implement C++ std::make_index_sequence reverse version. To get - make_index_sequence_reverse<int, 5> = <4,3,2,1,0> . Thank you! 回答1: IMHO, there is no reason for a index_sequence_reverse : std::index_sequence support sequences of indexes and are order neutral (or even without order). If you can use std::make_index_sequence , for a makeIndexSequenceReverse you can make something as follows #include <utility> #include <type_traits> template <std::size_t ... Is> constexpr auto

问题 Who knows how to implement C++ std::make_index_sequence reverse version. To get - make_index_sequence_reverse<int, 5> = <4,3,2,1,0> . Thank you! 回答1: IMHO, there is no reason for a index_sequence_reverse : std::index_sequence support sequences of indexes and are order neutral (or even without order). If you can use std::make_index_sequence , for a makeIndexSequenceReverse you can make something as follows #include <utility> #include <type_traits> template <std::size_t ... Is> constexpr auto

问题 Is there a difference between: template <class T> constexpr decltype(auto) f(T&& x) -> decltype(std::get<0>(std::forward<T>(x))) { return std::get<0>(std::forward<T>(x)); } and: template <class T> constexpr auto f(T&& x) -> decltype(std::get<0>(std::forward<T>(x))) { return std::get<0>(std::forward<T>(x)); } and if so, what is it, and which one should I use for perfect forwarding? 回答1: Trailing return type should only be used with auto The point of decltype(auto) vs auto is to distinguish the

问题 Previous question. I repeat the code from the previous question to make this question self-contained. The code below compiles and does not issue any warnings if it is compiled using gcc 4.8.3. with -std=c++1y . However, it does issue warnings if compiled with -std=c++0x flag. In the context of the previous question it was stated that the code does not compile using gcc 4.9.0. Unfortunately, at present, I do not fully understand how auto is implemented. Thus, I would appreciate if anyone could

问题 I'd like a constexpr function that will return me a unique id for every C++ type, something like this: using typeid_t = uintptr_t; template <typename T> constexpr typeid_t type_id() noexcept { return typeid_t(type_id<T>); } int main() { ::std::cout << ::std::integral_constant<typeid_t, type_id<float>()>{} << ::std::endl; return 0; } But I get an error: t.cpp: In function 'int main()': t.cpp:23:69: error: conversion from pointer type 'typeid_t (*)() noexcept {aka long unsigned int (*)()

问题 In comments to this question is-there-a-way-to-iterate-over-at-most-n-elements-using-range-based-for-loop there was additional question - is this possible to have "index view" on a container, i.e. to have subrange with some indexes filtered out. Additionally I encountered a problem to find minimum value from a range with some indexes filtered out. I.e. is it possible to replace such code as below with std and/or boost algorithms, filters - to make it more readable and maintainable: template

问题 Isn't it better to use std::declval declared in form: template< class T > T declval(); // (1) then current one: template< class T > T && declval(); // (2) for std::common_type (possibly with different name only for this current purpose)? Behaviour of common_type using (1) is closer to the behaviour of the ternary operator (but not using std::decay_t ) than the behaviour when using (2) : template< typename T > T declval(); template <class ...T> struct common_type; template< class... T > using