930 questions
10
votes
1
answer
515
views
Is this a well-defined way to access bitfield bits by index in C11
The order of bits in C11 bitfields is implementation-defined, and so is any padding in between them. This makes it difficult to access the bitfields by index at runtime, even though most ...
- 12.5k
3
votes
1
answer
94
views
Casting pointer-to-intptr_t to pointer-to-pointer
A pointer can be safely cast to intptr_t (or uintptr_t) and back (on platforms where those types exist), but what about casting a pointer-to-intptr_t into pointer-to-pointer and using that to modify ...
- 2,540
1
vote
1
answer
198
views
Why does this ANTLR4 grammar complain about C code that is obviously legal and compilable?
I'm writing a tool in Kotlin using ANTLR4 with this nicely working grammar:
Grammar for C11 by Sam Harwell
The grammar works fine, my tool works. But suddenly I ran into a problem. One C source made a ...
- 396
1
vote
1
answer
145
views
Tagging pointers & well-defined ways to create a misaligned pointer
C11 6.3.2.3p7 says:
A pointer to an object type may be converted to a pointer to a
different object type. If the resulting pointer is not correctly
aligned 68) for the referenced type, the behavior ...
- 60.6k
1
vote
2
answers
120
views
Why std=c11 allows using of nonstandard functions?
I can compile and run a program that includes <getopt.h> and uses getopt_long with keys -std=c11 --pedantic-errors. Can you explain why?
- 163
2
votes
1
answer
125
views
C11: are rules of reserved identifiers irrelevant if library is not used?
In C11 rules of reserved identifiers are defined in the library clause (clause 7).
Hence, are rules of reserved identifiers irrelevant if library is not used?
Note: in C23 rules of reserved ...
- 6,757
4
votes
1
answer
104
views
The sequential consistent order of C++11 vs traditional GCC built-ins like `__sync_synchronize`
So I've came across Jeff Preshing's wonderful blog posts on what's Acquire/Release and how they may be achieved with some CPU barriers.
I've also read that SeqCst is about some total order that's ...
- 63
2
votes
4
answers
171
views
Is { struct-declaration-list } a block?
Is { struct-declaration-list } in C11 (as known as { member-declaration-list } in C23) a block?
The original issue: I cannot find the exact definition of the term "block" in the C standard (...
- 6,757
2
votes
1
answer
85
views
Does the the 2+2W litmus test code in the 'Repairing Sequential Consistency' paper have a problem?
I was reading the paper Repairing Sequential Consistency in C/C++11 by Lahav et al and had a doubt regarding the 2+2W litmus test presented there.
Under the section Semantics of SC Atomics in C11, ...
- 1,352
6
votes
1
answer
220
views
Can a C compiler legally reject a program if its call stack depth exceeds a fixed limit at compile time?
I've read that C doesn't mandate a minimum stack size, leaving it implementation-defined. But could a conforming C compiler refuse to compile a program if it detects--say, through static analysis--...
- 506
1
vote
1
answer
102
views
Does assigning a volatile variable to itself suppress compiler optimization in a loop?
I'm working on a delay loop in C and come across an odd case with volatile. Consider this code:
void delay(unsigned int count){
volatile unsigned int timer = count;
while (timer > 0){
...
- 506
2
votes
2
answers
138
views
Function-like macro in C11 _Generic
I would like to use _Generic to expand function-like macro instead of function in C:
#include <stdio.h>
#define VAL_V(X) X
#define VAL_P(X) *X
#define VAL(X) _Generic((X), int: VAL_V, int *: ...
- 887
1
vote
1
answer
158
views
Require trailing comma
My application is written in C99 (or rather GNU99, and I wouldn't mind going to GNU11), and I'd like to require trailing commas in structure initializers. Does GCC have a warning (turned into error ...
- 5,926
0
votes
4
answers
140
views
Using = operator on atomic variable?
Is newNode->next = NULL; an undefined behavior in this case?
struct node {
int value;
_Atomic(struct node*) next;
};
//at the initialization stage
struct node* newNode = malloc(sizeof(struct ...
3
votes
1
answer
189
views
Math error conditions (C99, C11, etc.) in GCC
With ISO C99 onward we have a few macros (or constants) that help understanding how some math errors (see <math.h> related) are signaled. However, to me it looks like they haven't been ...
- 433