c++17

问题 After I had solved my issue to this question I went on to expand this version of my code to incorporate the unions of the data fields from my previous template versions with this version and I have this so far: main.cpp #include <iostream> #include <type_traits> #include "Register.h" int main() { using namespace vpc; std::cout << std::boolalpha; std::cout << "std::bitset<64> is trivially copyable " << std::is_trivially_copyable<std::bitset<64>>::value << '\n' << "QWord is trivially copyable "

问题 I have a class template, and I do not know if I need to have as one of its arguments class Func or not. I also do not know if I can arbitrarily store a std::function directly into a container without its template argument parameter list. My class looks something like: template<class Data, class Func> class ThreadManager final { private: std::vector<std::shared_ptr<Data>> storedDataPtrs; std::vector<std::shared_ptr<std::thread>> storedThreadPtrs; // Is this valid? I know that `std::function is

问题 What am I missing here? Why can't I use decltype to define the value_type of an iterator? The code below gets inscrutable compile-time errors when I use decltype rather than iterator_traits, but only if I also use value_type to declare a vector. Visual Studio 2017, C++17 rev. 15.6 Preview #include <vector> template<class Ptr > void foo(Ptr beg) { *beg = 1; // Cool, babies. // using value_type = decltype(*beg); // COMPILER ERROR when buf declared below using value_type = typename std::iterator

问题 'Concepts lite' were already accepted as a TS and (example implementation) merged into GCC main branch, so the follow up question is will any concepts come predefined (like Sortable or Random_access_range )? Where do I look for such predefined concepts? Is the list at cppreference.com an acurate and exhaustive list? Can I use them with the latest GCC trunk build? Edit 1 : Changed C++17 to TS due to concepts not being accepted into C++17. 回答1: There are no concepts defined in the Concepts TS

问题 Considering type A : template <typename T, size_t N> struct A { T arr[N]; }; Is there any difference between C++17 user-defined deduction guides template <typename T, typename ... Ts> A(const T&, const Ts& ...) -> A<T, 1 + sizeof...(Ts)>; and template <typename T, typename ... Ts> A(T, Ts ...) -> A<T, 1 + sizeof...(Ts)>; ? Or, in other words is there any difference between const references and values in deduction guides? Please note that the question is not about template function type

问题 The following simple test case file is giving me a compile-time error with the tip of 'master' from Clang's github mirror, when compiled with -fmodules , using the command shown below. I'm wondering if this is a bug with the new experimental Module feature for Clang -- maybe a problem with the implementation of module maps for the standard library -- or if there's something I'm doing wrong. The error still appears if I add -fbuiltin-module-map to the command. Interestingly, the error no

问题 Consider this example: template <typename T> using type = typename T::type; template <typename T> struct A { A(type<T>); }; A<int> f(); A<int> g() { return f(); } Neither gcc nor clang compile this code due to int not having a nested type typedef. But why is that constructor being instantiated at all? f() is a prvalue of the same type as the return of g() , there shouldn't even be a move there. What is causing us to instantiate the bad constructor? 回答1: The constructor is a bit of a red

问题 i am new to c++. i compiled my code in visual-studio-code in windows10, with 2 variables of type string and string_view. string variable is fine, but string_view is giving errors.I also enable c++17 extension in configuration.json and edit configuration/ui file in vscode. Here is my code:= #include<iostream> #include<string_view> using namespace std; int main(){ string str="hello"; cout<<str<<endl; std::string_view sv=" world"; auto result=str+sv.data(); return 0; } errors are:= main.cpp: In

问题 W.F. gave a now-deleted answer to my question here which used the line: auto [x, y] = div_t{ 1, 0 }; From the code in the answer it looks like that's like a tie for the div_t struct. I was hoping that someone could explain what was going on here. The complete function code was as follows: constexpr bool first_quot() { auto [x, y] = std::div_t{1, 0}; (void)y; return x; } 回答1: In the most most recent draft of the C++17 specification it's called "Decomposition declarations" and is defined in

问题 I'm trying to create a multi-dimensional array with dynamic memory initialisation in C++, but an implicit type conversion works in one way when I work directly with functions, but in another way when I tried to create class-shell around this pointer and named functions as class members. If template type T, for example, int, with structures it prefers (T *&) type over (T &) for a pointer of any nesting, but when I made these functions class members, they even can't implicitly make T** to (T*&)