#include <iostream> struct U { template<typename T> operator T(); }; template<unsigned I> struct X : X<I – 1> {}; template<> struct X<0> {}; template<typename T> constexpr auto f(X<4>) -> decltype(T(U{}, U{}, U{}, U{}), 0u) { return 4u; } template<typename T> constexpr auto f(X<3>) -> decltype(T(U{}, U{}, U{}), 0u) { return 3u; } template<typename T> constexpr ..
Category : aggregate-initialization
struct BasePluginInfo { bool bHasGui, bIsSynth; char cType; std::string sCategory, sSdkVersion, sVendor, sVersion; }; struct PluginClassInfo { std::string sName, sUid; std::vector<std::string> vsParamNames; }; struct ShellPluginInfo : BasePluginInfo { std::vector<PluginClassInfo> vciClasses; }; When I do ShellPluginInfo { .bHasGui = true }; The compiler complains that ShellPluginInfo has no field ‘bHasGui’. However this works: ShellPluginInfo info; info.bHasGui ..
In the following code there is an initialization of A<T> objects with template argument deduction using two forms distinct by the type of braces: template<typename T> struct A{ T x; }; int main() { static_assert( A{1}.x == 1 ); //#1: ok in GCC and MSVC static_assert( A(1).x == 1 ); //#2: ok in GCC only ..
In the following code there is an initialization of A<T> objects with template argument deduction using designated initializers in two slightly distinct forms: template<typename T> struct A { T t; }; int main() { A a{.t=1}; //#1: ok in GCC and MSVC A b{.t={1}}; //#2: ok in MSVC only } The first way is accepted ..
typedef struct node { int val; int val2; node(int a, int b) : val(a), val2(b) {} node(int val) = delete; }node; int main() { node a = {3}; cout << a.val << " " << a.val2 << endl; return 0; } The above code gives compile error showing that use of deleted function node::node(int). However, ..
Here’s the setup to illustrate the problem. template <typename T> struct opt { const char* name; T x; template <typename X> opt(const char* name, X&& x) : name(name), x(std::forward<X>(x)) { } }; template <typename T> opt(const char*, T&&) -> opt< some_type_transformation<T> >; template <typename… T> void function(opt<T>&&… opts) { // do something with the passed ..
C++20 introduced support for designated initializers. In g++ with -std=c++17, one can use designated initializers and as long as you don’t leave any out, it will compile without any errors or warnings: struct Foo { int a; float b; }; Foo f { .a = 7, .b = 42.1f, }; Yet if I enable -Wpedantic ..
In the following program the union U has two fields a and b, each with distinct default value. If one creates a variable of type U using aggregate initialization {} what are the value and the active member of the union? #include <iostream> struct A { int x = 1; }; struct B { int ..
Please consider the code with aggregate struct B having a field of class A with a private constructor: class A { A(int){} friend struct B; }; struct B { A a{1}; }; int main() { B b; //ok everywhere, not aggregate initialization //[[maybe_unused]] B x{1}; //error everywhere [[maybe_unused]] B y{}; //ok in GCC and Clang, ..
I have a struct struct RGB { int r; int g; int b; } I know that aggregate initialization can be used: RGB rgb = {255, 255, 255}; I wonder if it is possible to initialize it using an array. I’ve tried these solutions and they do not work: int rgb_array[] = {255, 255, 255}; ..
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