language-lawyer

来源： https://stackoverflow.com/questions/63061188/what-are-the-rules-for-standard-library-containers-and-incomplete-types

来源： https://stackoverflow.com/questions/63061188/what-are-the-rules-for-standard-library-containers-and-incomplete-types

来源： https://stackoverflow.com/questions/63551203/which-of-these-new-expressions-with-char-arrays-are-well-formed

来源： https://stackoverflow.com/questions/63551203/which-of-these-new-expressions-with-char-arrays-are-well-formed

来源： https://stackoverflow.com/questions/63551203/which-of-these-new-expressions-with-char-arrays-are-well-formed

来源： https://stackoverflow.com/questions/63489656/are-there-any-floating-point-requirements-concerning-precision-and-range-in-the

来源： https://stackoverflow.com/questions/53100198/what-is-the-precise-relationship-between-c-and-its-abstract-machine

来源： https://stackoverflow.com/questions/63618919/difference-in-overload-selection-of-user-defined-conversion-operator-between-cla

问题 As far as I'm aware, the following code: template<typename T> struct S { S<T>(); }; is well-formed, even though the <T> in the declaration of the constructor is redundant. However, on gcc trunk (but not on gcc10.2), with -std=c++20 this gives an error: error: expected unqualified-id before ')' token 3 | S<T>(); ^ The code compiles on clang trunk with -std=c++20 . Is this a bug, or is this a breaking change in c++20 that is yet to be implemented in all compilers? 回答1: There was a change, in

问题 template<typename T, typename U = T> struct Test{}; template<typename T> void func(Test<T>){ //#1 } int main(){ func(Test<int>{}); //#2 } Consider the above code, At the point of invocation of function template func , the type of argument is Test<int,int> , When call the function template, template argument deduction will perform. The rule of template argument deduction for function call is : temp.deduct#call-1 Template argument deduction is done by comparing each function template parameter