Introduction template<int F(), int N = F()> void func (); In this answer we will go through the relevant sections of the International Standard, step by step, to prove that the above snippet is well-formed. What does the International Standard (N3337) say? The Standardese 14.1p9 Template parameters [temp.param] A default template-argument is a template-argument (14.3) … Read more
Update: The situation got a bit more complicated after the resolution of CWG DR 1684 removed the requirement quoted below. Some more information can be found in this discussion on the std-discussion mailing list and in the related question Why isn’t `std::initializer_list` defined as a literal type? [decl.constexpr]/8: A constexpr specifier for a non-static member … Read more
To me it sounds like someone messed up merging the previous standard with the new one. Previously the standard said this: (C++14 N4140, 7.1.6.4.7 [dcl.spec.auto]): When a […] return statement occurs in a function declared with a return type that contains a placeholder type, the deduced return type or variable type is determined from the … Read more
This is a result of The Equality Operator You Are Looking For (P2468). The comparison changes in C++20 – which allow a == b and a != b to find rewritten and synthesized candidates – can break a lot of C++17 code. You can see some examples in the paper. In an effort to mitigate … Read more
In addition to the paragraphs quoted in the question, there is paragraph 6.4.4.5/3: The keywords false and true are constants of type bool with a value of 0 for false and 1 for true. and 6.6/7: An identifier that is: […] — a predefined constant; […] is a named constant That makes false a named … Read more
Can calloc() allocate more than SIZE_MAX in total? As the assertion “On select systems, calloc() can allocate more than SIZE_MAX total bytes whereas malloc() is limited.” came from a comment I posted, I will explain my rationale. size_t size_t is some unsigned type of at least 16 bits. size_t which is the unsigned integer type … Read more
From [dcl.fct], pretty explicitly: Functions shall not have a return type of type array or function, although they may have a return type of type pointer or reference to such things. There shall be no arrays of functions, although there can be arrays of pointers to functions. With C++11, you probably just want: std::function<int()> f(); … Read more
This is all 100% standardized. C17 6.10.8.1: __DATE__ The date of translation of the preprocessing translation unit: a character string literal of the form “Mmm dd yyyy” … and the first character of dd is a space character if the value is less than 10. … __TIME__ The time of translation of the preprocessing translation … Read more
Order of Left and Right Operands To perform the assignment in arr[global_var] = update_three(2), the C implementation must evaluate the operands and, as a side effect, update the stored value of the left operand. C 2018 6.5.16 (which is about assignments) paragraph 3 tells us there is no sequencing in the left and right operands: … Read more
From the current Standard draft ([basic.types.general]/2): For any object (other than a potentially-overlapping subobject) of trivially copyable type T, whether or not the object holds a valid value of type T, the underlying bytes ([intro.memory]) making up the object can be copied into an array of char, unsigned char, or std::byte ([cstddef.syn]). If the content … Read more