A non-owning lightweight wrapper object referring to a contiguous sequence of elements in memory
Questions tagged [std-span]
60 questions
5
votes
3 answers
Why can T not be deduced for std::span when passing a std::vector?
In the following C++20 code, passing a std::vector to a templated function with a std::span parameter fails, because obviously the compiler cannot deduce the template parameter. I have tried this with GCC, Clang and MSVC; all fail.
Invoking like…
FrankM
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5
votes
1 answer
Why C++20 knows how to hash string_view, but does not know how to hash span?
My best guesses are that committee either forgot about this use case or did not want to use concepts/requires to restrict the span type to something that can be safely hashed(POD, no padding), or they did not want half solutions(waiting for…
NoSenseEtAl
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5
votes
2 answers
Convert a nullptr to std::span
I have a const z* zs = nullptr;
I want to convert zs to std::span
When I try to do std::span(zs) I get an error saying
error: no matching function for call to ‘std::span::span(const z* const&)’
How do I convert to zs to…
TeenyTinySparkles
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4
votes
1 answer
Create std::string from std::span of unsigned char
I am using a C library which uses various fixed-sized unsigned char arrays with no null terminator as strings.
I've been converting them to std::string using the following function:
auto uchar_to_stdstring(const unsigned char* input_array, int…
Simog
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4
votes
1 answer
Can std::span iterators outlive the span object they are created from?
Put it other way, conversely, are std::span iterators invalidated after the span instance is destroyed?
I have a vector I need to iterate over with different layouts. I'm trying to make use of std::span to avoid writing a lot of iterator boilerplate…
ofo
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4
votes
4 answers
Generic function using std::span doesn't compile
I wanted to make an isIn function that takes an std::span.
This is my attempt:
#include
template
bool isIn(const T1& x, std::span v)
{
for (const T2& e : v)
if (e == x)
return…
tuket
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3
votes
3 answers
What is the idiomatic way to create a fixed size std::array from a fixed size std::span?
I am trying to create a std::array from a std::span but I cannot find a way to do so without memcpy, std::copy, or std::ranges::copy which don't protect me against wrong specification of destination array size.
#include…
phinz
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3
votes
1 answer
C++20 std::span: Uses of converting constructor
The converting constructor of C++ std::span of the form:
template
constexpr explicit(see below) span(
const span& s) noexcept;
with constraints, can be used for the…
cbhattac
- 121
- 4
3
votes
1 answer
Why does C++ span's C style array constructor need type_identity_t?
The C style array constructor for span is specified as follows
template constexpr span(
type_identity_t (&arr)[N]) noexcept;
Why is type_identity_t necessary? instead of just:
template constexpr span(
…
cbhattac
- 121
- 4
3
votes
1 answer
What is an mdspan, and what is it used for?
Over the past year or so I've noticed a few C++-related answers on StackOverflow refer to mdspan's - but I've never actually seen these in C++ code. I tried looking for them in my C++ compiler's standard library directory and in the C++ coding…
einpoklum
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3
votes
2 answers
what is the way to remove the first element from a std::span?
when reading the document of std::span, I see there is no method to remove the first element from the std::span.
Can you suggest a way to solve my issue?
The large picture of my problem(I asked in another question: How to instantiatiate a…
ollydbg23
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3
votes
1 answer
How to initialize std::span? Problems with const-ness
I am trying to initialize a span — that is, a list of pointers to const data.
However, the rules for const conversion amongst pointers and span<>'s available constructors are thwarting me.
I'm sure there's a way to do it, but I cannot find…
jwd
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3
votes
1 answer
Is std::span a view?
Is std::span a view?
My speculation stems from the fact that it does not "own".
I have read that it is a reference to ranges here and that it "just wraps" I have not seen anywhere been stated explicitly that it is a view.
gonidelis
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3
votes
1 answer
Is there a common pattern for passing vector as span?
I don't think there's any getting away from the need to allocate a buffer to hold the span of string_views. So probably an intermediate std::vector? Any good overall pattern to crush it down to 1 line? If necessary, what kind of…
VoidStar
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3
votes
2 answers
Is using std::span into an std::vector after push_back is called undefined behavior
My understanding of std::span is that it is essentially contains pointer into a container, a size, and some useful member functions.
template
class SimpleSpan {
T* ptr;
size_t length;
// some member functions
}
I can take a…
user542101
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