All Questions
Tagged with c++ language-lawyer
6,453
questions
3
votes
1
answer
100
views
std::variant::operator< unexpected call to implicit bool conversion. Varies between standards
I'm seeing some unexpected behavior when using the std::variant::operator<. In the situation where the type has an implicit bool conversion operator and its less operator is not a member function (...
- 9,492
2
votes
0
answers
39
views
Is the initialization of an object a modification to a memory location when considering conflict actions?
struct A{int a; A():a(1){}}
std::atomic<A*> x;
// thread 1:
A* ptr = new A(); // #1
x.store(ptr,memory_order::relaxed);
//thread 2:
auto ptr = x.load(memory_order::relaxed);
int b = ptr-&...
- 7,280
1
vote
1
answer
84
views
consteval member function allowed?
I have this c++20/23 code:
#include <cstddef>
template <size_t N>
class Foo {
public:
consteval size_t size() noexcept { return N; }
size_t real_size() {
...
- 2,587
2
votes
1
answer
72
views
Order of c++ template arguments affecting compilation
I just encountered a new compilation error in my code after a visual studio update. I have stripped my code down to what I think is a minimal example. I have two templated functions both called pow - ...
- 1,757
6
votes
2
answers
150
views
In C++26, are implementations required to "initialize" uninitialized variables to some fixed byte pattern?
In C++26, reading uninitialized variables is no longer undefined, it's "erroneous" now (What is erroneous behavior? How is it different from undefined behavior?).
However, the wording for ...
- 91.2k
2
votes
1
answer
63
views
Is `AcqRel` necessary in the atomic read-modify-write operation to avoid data race in a lock-free multi-producer single consumer queue?
Consider this snippet code of implementing a lock-free multi-producer single-consumer queue in Rust
struct Node<T> {
next: AtomicPtr<Node<T>>,
value: Option<T>,
}
impl&...
- 7,280
4
votes
2
answers
110
views
Move elision in explicit object member functions
If one calls explicit object member function of a temporary, must the move of the temporary be elided in the explicit object parameter?
Consider the following example, where struct A has move ...
- 19.3k
-1
votes
1
answer
49
views
tool do determine the value category an expression: understanding the result when using references
Looking into definition of value-categories, I tried a snippet proposed here: https://stackoverflow.com/a/16638081/21691539
template <typename T>
struct value_category {
// Or can be an ...
- 1,708
4
votes
1
answer
83
views
Can I use template parameters to refer to base class member functions?
I'm trying to understand why this code doesn't compile with GCC but compiles with MSVC:
template<class TParams>
class Selector : public TParams::DataSource1, public TParams::DataSource2
{
...
- 1,078
2
votes
1
answer
95
views
Overload resolution between ordinary and explicit object member functions
In the following test program, struct B has two member functions f, which can be called using B{}.f(): one ordinary f() and another with explicit object f(this A).
struct A {
int f() { return 1; }
...
- 19.3k
5
votes
1
answer
99
views
On which member is no_unique_address needed and why?
Consider the following two structs whose sizes are 8 and 1 bytes respectively:
class eight {
int i;
char c;
eight(const blub&) {}
};
class one {
char s;
one(const blob&...
- 63.7k
10
votes
0
answers
206
views
Semantics of volatile std::atomic<T>
Generally std::atomic<T> does not imply semantics of volatile, i.e. operations on the atomic object are not observable side effects that the compiler needs to preserve.
As a consequence the ...
- 66.4k
0
votes
1
answer
53
views
How does C++ handle constexpr evaluation for non-static member function pointers on runtime objects?
The code compiles and runs, but I'm trying to understand how the expression (obj.*funcPtr)(12) can be evaluated at compile-time when obj is not declared as constexpr. I would expect that this might ...
- 693
-3
votes
1
answer
101
views
is there any UB in reinterpreting a standard layout struct as an unsigned char* [closed]
I wanted to see if it is safe to reinterpret_cast a Colour struct
array into an unsigned char* to pass around for APIs
struct Colour {
unsigned char r,g,b,a;
};
static_assert(sizeof(Colour) == ...
- 329
3
votes
1
answer
126
views
Explicit object member function with void parameter
According to cppreference since C++23
For a non-static non-virtual member function not declared with cv-qualifier or ref-qualifier, its first parameter, if not being a function parameter pack, can be ...
- 19.3k