A library for C++20 that introduced std::ranges namespace, which consists of rangified algorithms from
Questions tagged [std-ranges]
379 questions
7
votes
2 answers
Why can't I use istream_view and std::accumulate to sum up my input?
This program:
#include
#include
#include
int main() {
auto rng = std::ranges::istream_view(std::cin);
std::cout << std::accumulate(std::ranges::begin(rng), std::ranges::end(rng), 0);
}
is supposed to sum…
einpoklum
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6
votes
1 answer
Is it still impossible to sort a range with proxy iterators whose value_type/reference is pair in C++23?
Although P2321 zip provides the common_reference specialization for pair, and P2165 Compatibility between tuple, pair and tuple-like objects makes tuple and pair interconvertible, the comparison function of pair only has the following candidates in…
康桓瑋
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6
votes
1 answer
Is there a way to determine if a range is constructed correctly?
I encountered unexpected behavior when mixing the output of boost::join with std::views::transform (shown below). The compiler issues no warnings whatsoever. Fortunately, an address sanitizer detects an invalid memory access in get2b().
The…
MarkB
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6
votes
1 answer
Using C++20 Ranges to Avoid Loops
I was assigned a task where I need to solve a problem given several constraints. The point is to enforce the use of STL algorithms, iterators, and new c++20 functionality including things like ranges. However I've been reading on ranges for hours…
Adham
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- 7
6
votes
0 answers
Is there a fundamental performance cost to using std::views::join?
I've recently been doing some performance evaluation of ranges & views. I've posted a simple example (also at https://www.godbolt.org/z/7ThxjKafc) where the difference in assembly is much more significant than I would have expected.
With latest GCC…
MarkB
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6
votes
1 answer
why I can't use a take() after a istream_view in c++20
The code shows my problem, I can't use take(3) after istream_view.
The error message is:
/home/linuxbrew/.linuxbrew/Cellar/gcc/11.1.0_1/include/c++/11.1.0/ranges:1775:48: error: passing…
Jiangqiu Shen
- 81
- 1
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6
votes
2 answers
ranges::view::transform produces an InputIterator preventing the use of std::prev
Consider the following code, which uses the Ranges library from C++20:
#include
#include
#include
int main()
{
std::vector v{0,1,2,3,4,5,6,7};
auto transformed = std::ranges::views::transform(v, [](int i){…
lisyarus
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6
votes
2 answers
Why is ranges::basic_istream_view::begin() not cached?
I found that c++20 ranges::basic_istream_view is slightly different from the range-v3 version.
The most important difference is that the std::ranges::basic_istream_view does not cache its begin(), so that each begin()s will return the next iterator…
康桓瑋
- 33,481
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6
votes
1 answer
How to support range adaptors in custom container?
I have created a custom container called goldbox that only contains arithmetic types and I have also implemented begin and end member functions to iterate over the elements.
My Full Source Code:
#include
#include
#include…
Desmond Gold
- 1,517
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6
votes
1 answer
Generator called twice in C++20 views pipeline
Here in a simple pipeline of views adaptors, there is the gen function called to generate a sequence of values (using an internal state) and then a filter on it.
What is surprising and counterintuitive (at least for me) is the fact that the…
Pascal H.
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6
votes
0 answers
C++20 views::join goes into an infinite loop on generated nested ranges::single_view
I'm playing with C++20 ranges with GCC implementations (v10.2 & v11).
To test the behavior of std::views::join, I tried to generate a nested view using single and then I flat it using join.
#include
#include
int main() {
auto…
Pascal H.
- 1,431
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6
votes
1 answer
Why can views::reverse transform a non-sized_range into a size_range?
In [range.sized#1]:
The sized_range concept refines range with the requirement that the
number of elements in the range can be determined in amortized
constant time using ranges::size.
template
concept sized_range =
range &&
…
康桓瑋
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6
votes
1 answer
std::ranges::copy will not accept std::vector in visual studio
The code below does not compile in Visual Studio, giving
Error C2672 'operator __surrogate_func': no matching overloaded function found sortms C:\Users\David\source\repos\sortms\sortms.cpp 103
The function works as written when I use a C-style…
davidbear
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6
votes
1 answer
what are the constraints for std::ranges::make_heap?
The following code works well with gcc:
struct S {
int i, j;
auto operator<(const S& s) const {
return i < s.i;
};
};
std::vector v;
std::make_heap(v.begin(), v.end());
But when I switch to C++20's range…
康桓瑋
- 33,481
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6
votes
1 answer
How to use ranges::sort for ascending or descending sort controlled by a boolean
Using ranges allowed me to reduce boilerplate, so it's great but I could not find a way sort either in ascending order or descending order.
The following snippet compiles just fine (g++ 10.2.0) and projection really simplifies the code, no need for…
user3636086
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