Questions tagged [c23]
C23 is the informal name of the next standard of the C programming language. It replaces C17 and introduces some new features.
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Using _Generic to implement IS_POINTER(p) with rvalue in C23?
I want to implement IS_POINTER(P) using _Generic. Using this answer that implements IS_ARRAY(A) as a starting point, I have:
#define IS_POINTER(P) \
_Generic( &(P), \
typeof(*P) ** : ...
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5
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Can C23 endianness macros be used to determine the layout of a bit-field?
I've been reading about the new additions to the C standard, and I've come across macros for determining the compile-time endianness.
However the standard still states that
The order of allocation of ...
- 3
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2
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Plain C equivalent to Rust's unimplemented!() macros
Please note that this is not a question on C++, but on plain C
In Rust there is a handy macro unimplemented!() to let the runtime crash, to be used when a function is unimplemented.
I basically have ...
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Are int main() and int main(void) equivalent prototypes in C23?
C23 introduced new semantics in function declarators:
6.7.6.3 Function declarators
[...]
13 For a function declarator without a parameter type list: the effect is as if it were declared with a ...
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Is the C23 standard backward compatible?
Can C17 code be interpreted as C23 code? If not, what are the breaking changes?
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Is there any difference between the C23 _BitInt() and a non-bit-precise integer of the same width?
The upcoming C23 Standard adds a keyword _BitInt() which can be used, as I understand, to define an integer with a specific number of bits. However I could not find much information with regards to ...
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Why doesn't gcc 13 display the correct binary represenation?
While answering a question here, I made the following example:
#include <stdio.h>
#include <math.h>
int main (void)
{
float_t a = -248.75;
printf("%f\n", a);
unsigned ...
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1
answer
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does offsetof work with typeof if type is new?
I read on cppreference (https://en.cppreference.com/w/c/types/offsetof):
Even though it is specified in C23 that defining a new type in
offsetof is undefined behavior, such usage is only partially ...
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votes
5
answers
272
views
How to use typeof_unqual to avoid compiler warnings about discarding const qualifier
In the following code, copyThing() is written so that its return value has the same type as its argument value:
extern void *copyThingImpl(const void *x);
#define copyThing(x) ((typeof(x)) ...
- 36.3k
10
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2
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280
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Does nullptr_t break type punning or pointer conversions?
Consider this union:
typedef union
{
void* vptr;
nullptr_t nptr;
} pun_intended;
nullptr_t is supposedly compatible with void* 1). Ok so what if we initialize the void* to some non-zero ...
- 208k
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How can I use "nullptr" for null pointers prior to C23?
In C23, the nullptr keyword got standardized. I would prefer to use nullptr instead of NULL prior to C23 too because it means that I could write code which compiles in:
C, prior to C23
C, since C23
C+...
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3
votes
2
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310
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Is there an equivalent of __attribute__((nonnull)) in C23?
Several compiler vendors have implemented a non standard extension __attribute__((nonnull)) to specify that a pointer must not be a null pointer.
C99 introduced a new syntax to specify that a function ...
- 142k
3
votes
1
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Can strlen be [[unsequenced]]?
The wording of the C23 working draft on unsequenced functions is unclear to me. Among other properties, unsequenced functions have to be independent:
(6) An object X is observed by a function call
(...
- 36.1k
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What are the [[reproducible]] and [[unsequenced]] attributes in C23, and when should I use them?
C23 introduced the attributes [[reproducible]] and [[unsequenced]].
What is the motivation behind them?
How are they defined, and what effect do they have on a function?
What kind of functions should ...
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What is the difference between C++11's constexpr and C23's [[reproducible]]?
C++11 added the constexpr keyword which can be added to functions to specify constant behavior.
C23 added what seems to be identical functionality in the form of the [[reproducible]] tag.
How are ...
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