c11

When answering a comment to another answer of mine here , I found what I think may be a hole in the C standard (c1x, I haven't checked the earlier ones and yes, I know it's incredibly unlikely that I alone among all the planet's inhabitants have found a bug in the standard). Information follows: Section 6.5.3.4 ("The sizeof operator") para 2 states "The sizeof operator yields the size (in bytes) of its operand" . Para 3 of that section states: "When applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1" . Section 7.20.3.3

C99 §6.5 Expressions (1) An expression is a sequence of operators and operands that specifies computation of a value, or that designates an object or a function, or that generates side effects, or that performs a combination thereof. (2) Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. 72) Furthermore, the prior value shall be read only to determine the value to be stored. 73) with the footnotes 72) A floating-point status flag is not an object and can be set more than once within an expression. 73)

I have a union in C like this: union AUnion { struct CharBuf { char *buf; size_t len; } charbuf; uint8_t num; double fp_num; }; My question is, can I guarantee that if given the following: union AUnion u; Then the following are true: &u == &u.num &u == &u.fp_num &u == &u.charbuf I.e they all start at the beginning of the memory segment where u is stored. In the case of this C program compiled with gcc version 5.3.0 and -std=c11 the above is true: #include <stdio.h> #include <stdint.h> #include <stdlib.h> union AUnion { struct CharBuf { char *buf; size_t len; } charbuf; uint8_t num; double fp

Consider the following snippet: void f(void); void g(…) { … return f(); … } Is this return f(); valid according to C11? I am not advocating using this pattern: if it works at all, it is obviously equivalent to f(); return; (where the return; itself would be redundant if this is at the end of function g() ). I am asking this question in the context of the static analysis of C programs, where the C code has already been written by someone else and the question is deciding whether or not it is valid according to the standard. I would interpret C11 6.8.6.4:1 as meaning that it is non-standard and

I read this question about noreturn attribute, which is used for functions that don't return to the caller. Then I have made a program in C. #include <stdio.h> #include <stdnoreturn.h> noreturn void func() { printf("noreturn func\n"); } int main() { func(); } And generated assembly of the code using this : .LC0: .string "func" func: pushq %rbp movq %rsp, %rbp movl $.LC0, %edi call puts nop popq %rbp ret // ==> Here function return value. main: pushq %rbp movq %rsp, %rbp movl $0, %eax call func Why does function func() return after providing noreturn attribute? Sourav Ghosh The function