Questions tagged [language-lawyer]
For questions about the intricacies of formal or authoritative specifications of programming languages.
language-lawyer
8,387
questions
2
votes
1
answer
91
views
Is comparing two pointers to different char objects undefined in C?
This is code of memmove from https://github.com/gcc-mirror/gcc/blob/master/libgcc/memmove.c
void *
memmove (void *dest, const void *src, size_t len)
{
char *d = dest;
const char *s = src;
if (d &...
- 735
1
vote
1
answer
69
views
Side effects of constructing an explicitly unused object
Say I have a struct that provides a method that does some work (has useful side effects) and then returns an instance of itself. Do I have to use that instance somehow in order to guarantee that the ...
- 2,471
4
votes
0
answers
63
views
What exception guarantee level does std::vector::operator=() have? [duplicate]
When I assign one std::vector to another std::vector, and std::bad_alloc raises internally, does the C++ specification guarantee that my vector will be left in the correct state? Does it have a basic ...
3
votes
1
answer
79
views
Can you call virtual methods on a base class in a union when a derived class is active?
While std::variant is great for some use cases, it's a bit analogous to std::tuple in that you can't name each individual variant. Often a struct is better than a tuple.
I'm wondering if it's legal ...
- 4,352
2
votes
2
answers
87
views
`static_cast<const bool&>` with `explicit operator bool`
Consider the following:
struct C {
explicit operator bool() const {
return true;
}
};
int main() {
C c;
auto b = static_cast<const bool &>(c);
return 0;
}
...
- 3,204
4
votes
1
answer
208
views
+400
Explicit object member function discrepancies between different compilers
I wrote the following program in c++23. Here I've overloaded member functions. But for all cases different compilers give different result as shown below in comment. As you can see I have three cases ...
- 1,120
0
votes
0
answers
59
views
Is it legal to pass two views to ranges::views::concat such that iterating on the first view will shrink the range backing up the second view?
Here's a small (ok, maybe not minimal) example
#include <range/v3/view/concat.hpp>
#include <range/v3/view/transform.hpp>
#include <unordered_set>
#include <vector>
#include &...
- 26.7k
0
votes
1
answer
68
views
Is GCC correct in rejecting overload between ref-qualified and non-ref-qualified member function? [duplicate]
If I understand this correctly, [over.load] doesn't exist in c++23, and so what I read in [over.load]/2.3 should not be true anymore, so this code
struct Foo {
int const& bar() const;
int bar()...
- 26.7k
2
votes
1
answer
98
views
Why are reference types not considered during operator method lookup?
Today I stumbled across the following oddity of Rust's operator/method lookup:
use std::ops::Add;
use std::fmt::Debug;
#[derive(Debug)]
struct Foo(i32);
impl Add for &Foo{
type Output = ...
- 3,498
47
votes
5
answers
7k
views
Can you find a real example of "time travel" caused by undefined behaviour? [closed]
I am curious. Does anyone know a non-hypothetical C or C++ counterexample to the myth that "the impact of the undefined behaviour is limited to code which runs after the line with undefined ...
- 1,534
13
votes
1
answer
515
views
Why destructor needs to be accessible even when it is not called?
Having class X, the following object initialization:
new (ptr) X(X());
requires an accessible destructor even since C++17. Why is that, when the object is initialized by the default constructor ...
- 23.1k
1
vote
0
answers
85
views
when unique_ptr implements pimpl, assignment in a class declaration also results in: error: invalid application of 'sizeof' to incomplete type '***'
excuse me, when I was implementing pimpl with std::unique_ptr, I accidentally found that when I set pimpl to nullptr in the header file, gcc(version 9.4.0,14.1.0) cannot be compiled. But cl.exe (...
- 11
2
votes
1
answer
159
views
Explicit this member function use accepted by msvc but rejected by clang and gcc
I wrote the following program that compiles with msvc but rejected by clang and gcc. It uses explicit object member function. Demo.
#include <iostream>
struct C{
int f(this int);
};
...
- 1,120
1
vote
2
answers
60
views
get constexpr variable from a lambda function is fine , but compile fail (Visual C++) and fine (gcc) when such statement is in a new lambda
This code compiles fine in gcc, but fail in Visual C++.
MCVE = https://wandbox.org/permlink/SqNI85EospSrwm5T
int main() {
auto func_do1Pass2=[&]() {
return 8;
};
constexpr int ...
- 1,116
1
vote
1
answer
19
views
UML: Stereotypes of the Standard Profile
In the UML 2.5.1 specification under section 22 "Standard Profile", p. 721 of the PDF file, it says: "The Standard Profile specifies a set of predefined standard stereotypes. A ...
- 119