c11

Currently I have a macro to check a value is a type. #define CHECK_TYPE_INLINE(val, type) \ ((void)(((type)0) != (0 ? (val) : ((type)0)))) This is useful to be able to type-check macro args in some cases. But what if I were to check against multiple types? for example, to check if it's a struct Foo * or struct Bar * . Example, static inline _insert_item(struct List *ls, void *item) { /* function body*/ } /* type-checked wrapper */ #define insert_item(ls, item) \ (CHECK_TYPE_ANY(item, struct Foo *, struct Bar *), \ _insert_item(ls, item)) Is there some good way to do this? Since this is tagged

Can anybody advise why Visual Studio 2017 does not support the C11 new feature _Generic ? I found it is a very useful feature but cannot used in Visual Studio 2017. Below is the sample code: #include <stdio.h> #define MYTYPE(X) _Generic((X),\ int:"int",\ float:"float",\ double:"double",\ default:"other") int main(void) { int d = 5; printf("%s\n", MYTYPE(d)); printf("%s\n", MYTYPE(2.0*D)); return 0; } The complier will give below warnings and errors: 1>------ Build started: Project: Project1, Configuration: Debug Win32 ------ 1>predef.c 1>c:\users\mia\documents\c\listing 16.13\project1\project1

I can't seem to pass the arguments to functions expecting different arguments (or to other _Generic macros which implement a subset of the types of the first one). #define DEBUG_PRINT(x,...) _Generic((x), \ debug_print_options *: DEBUG_PRINT_CUSTOM_TYPE(x, __VA_ARGS__), \ default: DEBUG_PRINT_BASIC_TYPE(x, __VA_ARGS__)) #define DEBUG_PRINT_BASIC_TYPE(x,...) debug_print_printf_specifier((#x), (x), TYPE_TO_PRINTF_SPECIFIER(x), __FILE__, __LINE__, _my_func__, &((struct debug_print_options){__VA_ARGS__})) #define DEBUG_PRINT_CUSTOM_TYPE(x,...) debug_print_custom_to_debug_string((#x), (x), GET

Does the C11 standard (note I don't mean C++11) allow you to declare variables at any place in a function? The code below is not valid in ANSI C (C89, C90): int main() { printf("Hello world!"); int a = 5; /* Error: all variables should be declared at the beginning of the function. */ return 0; } Is it valid source code in C11? Yes. This was already valid in C99 (see the second bullet here ). More or less. C99 introduced the ability to declare variables part way through a block and in the first section of a for loop, and C2011 has continued that. void c99_or_later(int n, int *x) { for (int i =

Does below snippet invoke undefined behavior in case of an error? #include <stdio.h> int main() { int i; /* Indeterminate */ if (scanf("%d", &i) == 1) /* Initialize */ printf("%d\n", i); /* Success! Print read value */ else printf("%d\n", i); /* Input failed! Is printing `i` UB or not? */ return 0; } What if scanf fails, is an uninitialized variable accessed? EDIT Moreover what if I replace scanf("%d", &i) with my_initializer(&i) : int my_initializer(int *pi) { double room_temp_degc = get_room_temp_in_degc(); if(room_temp_degc < 12.0) { // Cool *pi = 42; return 1; } else { return 0; } } In C90

isspace() works if the input is representable as unsigned char or equal to EOF . getchar() reads the next character from stdin. When getchar()!=EOF ; are all getchar() returned values representable as unsigned char ? uintmax_t count_space = 0; for (int c; (c = getchar()) != EOF; ) if (isspace(c)) ++count_space; May this code lead to the undefined behavior? According to C11 WG14 draft version N1570 : §7.21.7.6/2 The getchar function is equivalent to getc with the argument stdin. §7.21.7.5/2 The getc function is equivalent to fgetc ... §7.21.7.1/2 [ !=EOF case] ...the fgetc function obtains that

I was looking into the C11 draft and it says An unnamed member of structure type with no tag is called an anonymous structure; an unnamed member of union type with no tag is called an anonymous union. The members of an anonymous structure or union are considered to be members of the containing structure or union. So I constructed the following testcase // struct type with no tag typedef struct { unsigned char a; unsigned char b; // ... Some other members ... unsigned char w; } AToW; union { AToW; // <- unnamed member unsigned char bytes[sizeof(AToW)]; } myUnion; Clang and GCC both complain