When are inline variables in static storage initialized?
来源： https://stackoverflow.com/questions/57437514/when-are-inline-variables-in-static-storage-initialized
inline-variable
When are inline variables in static storage initialized?
来源： https://stackoverflow.com/questions/57437514/when-are-inline-variables-in-static-storage-initialized
Are all constexpr variable implicitly inline?
问题 I was playing around with auto template parameters and I was surprised that this code didn't compiled: constexpr auto bar = 2; template<auto& T> struct Foo { auto operator()() const { return T; } }; int main() { Foo<bar> b; b(); } Visual Studio 15.7 (preview 4) spit out these errors: error C2970: 'Foo': template parameter 'T': 'bar': an expression involving objects with internal linkage cannot be used as a non-type argument note: see declaration of 'Foo' note: see declaration of 'bar' error
Are all constexpr variable implicitly inline?
问题 I was playing around with auto template parameters and I was surprised that this code didn't compiled: constexpr auto bar = 2; template<auto& T> struct Foo { auto operator()() const { return T; } }; int main() { Foo<bar> b; b(); } Visual Studio 15.7 (preview 4) spit out these errors: error C2970: 'Foo': template parameter 'T': 'bar': an expression involving objects with internal linkage cannot be used as a non-type argument note: see declaration of 'Foo' note: see declaration of 'bar' error
Are inline variables unique across boundaries?
问题 This is a follow up of this question. As mentioned in the comments to the answer: An inline variable has the property that - It has the same address in every translation unit . [...] Usually you achieved that by defining the variable in a cpp file, but with the inline specifier you can just declare/define your variables in a header file and every translation unit using this inline variable uses exactly the same object. Moreover, from the answer itself: While the language does not guarantee
Initializer “sizeof(T)” of inline static auto… Does it need instantiation?
问题 What should happen if an expression's type is not dependent, but we use it to initialize a static auto variable? GCC and Clang differ in their behavior template<typename T> struct A { static inline auto x = sizeof(T{}.f); }; A<int> a; GCC doesn't raise an error. But Clang thinks that this is invalid because it instantiates the operand of "sizeof". GCC appears to skip that step because sizeof(T{}.f) always has type size_t (not type dependent), so it already knows type of x without
Initializer “sizeof(T)” of inline static auto… Does it need instantiation?
What should happen if an expression's type is not dependent, but we use it to initialize a static auto variable? GCC and Clang differ in their behavior template<typename T> struct A { static inline auto x = sizeof(T{}.f); }; A<int> a; GCC doesn't raise an error. But Clang thinks that this is invalid because it instantiates the operand of "sizeof". GCC appears to skip that step because sizeof(T{}.f) always has type size_t (not type dependent), so it already knows type of x without instantiation. Both compilers conformly reject the program if we refer to x , for example by (void) a.x; . Does it
Why does cppreference define type_traits xxx_v shortcuts as inline constexpr and not just constexpr?
问题 Why does cppreference define type_traits xxx_v shortcuts as inline constexpr and not just constexpr ? For example, see is_integral_v: template< class T > inline constexpr bool is_integral_v = is_integral<T>::value; Is this just a matter of style or is there some difference in behavior? As far as I know constexpr variables are implicitly inline . Edit: Looking at the draft of the latest standard, it also uses inline constexpr . The question actually applies to the standard, then. 回答1: [basic
Are inline variables unique across boundaries?
This is a follow up of this question . As mentioned in the comments to the answer: An inline variable has the property that - It has the same address in every translation unit . [...] Usually you achieved that by defining the variable in a cpp file, but with the inline specifier you can just declare/define your variables in a header file and every translation unit using this inline variable uses exactly the same object. Moreover, from the answer itself: While the language does not guarantee (or even mention) what happens when you use this new feature across shared libraries boundaries, it does