Difference between revisions of "cpp/container/span/as bytes"
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m (→See also: reuse dsc.) |
Andreas Krug (Talk | contribs) m (fmt) |
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{{dcl header|span}} | {{dcl header|span}} | ||
{{dcl|num=1|since=c++20|1= | {{dcl|num=1|since=c++20|1= | ||
| − | template< class T, std::size_t N> | + | template< class T, std::size_t N > |
std::span<const std::byte, S/* see below */> | std::span<const std::byte, S/* see below */> | ||
as_bytes( std::span<T, N> s ) noexcept; | as_bytes( std::span<T, N> s ) noexcept; | ||
}} | }} | ||
{{dcl|num=2|since=c++20|1= | {{dcl|num=2|since=c++20|1= | ||
| − | template< class T, std::size_t N> | + | template< class T, std::size_t N > |
std::span<std::byte, S/* see below */> | std::span<std::byte, S/* see below */> | ||
as_writable_bytes( std::span<T, N> s ) noexcept; | as_writable_bytes( std::span<T, N> s ) noexcept; | ||
| Line 26: | Line 26: | ||
===Example=== | ===Example=== | ||
| − | {{example|code= | + | {{example |
| + | |code= | ||
#include <cstddef> | #include <cstddef> | ||
#include <iomanip> | #include <iomanip> | ||
| Line 45: | Line 46: | ||
/* mutable */ float data[1]{3.141592f}; | /* mutable */ float data[1]{3.141592f}; | ||
| − | auto const const_bytes = std::as_bytes(std::span{ data }); | + | auto const const_bytes = std::as_bytes(std::span{data}); |
print(data[0], const_bytes); | print(data[0], const_bytes); | ||
| − | auto const writable_bytes = std::as_writable_bytes(std::span{ data }); | + | auto const writable_bytes = std::as_writable_bytes(std::span{data}); |
// Change the sign bit that is the MSB (IEEE 754 Floating-Point Standard). | // Change the sign bit that is the MSB (IEEE 754 Floating-Point Standard). | ||
| − | writable_bytes[3] {{!=}} std::byte{ 0B1000'0000 }; | + | writable_bytes[3] {{!=}} std::byte{0B1000'0000}; |
print(data[0], const_bytes); | print(data[0], const_bytes); | ||
} | } | ||
| − | |p=true<!-- requires IEEE-754 format and little endian --> | + | |p=true<!--requires IEEE-754 format and little endian--> |
|output=<nowiki/> | |output=<nowiki/> | ||
3.14159 = { D8 0F 49 40 } | 3.14159 = { D8 0F 49 40 } | ||
Latest revision as of 00:01, 28 September 2023
| Defined in header <span>
|
||
| template< class T, std::size_t N > std::span<const std::byte, S/* see below */> |
(1) | (since C++20) |
| template< class T, std::size_t N > std::span<std::byte, S/* see below */> |
(2) | (since C++20) |
Obtains a view to the object representation of the elements of the span s.
If N is std::dynamic_extent, the extent of the returned span S is also std::dynamic_extent; otherwise it is sizeof(T) * N.
as_writable_bytes only participates in overload resolution if std::is_const_v<T> is false.
[edit] Return value
1) A span constructed with {reinterpret_cast<const std::byte*>(s.data()), s.size_bytes()}.
2) A span constructed with {reinterpret_cast<std::byte*>(s.data()), s.size_bytes()}.
[edit] Example
Run this code
#include <cstddef> #include <iomanip> #include <iostream> #include <span> void print(float const x, std::span<const std::byte> const bytes) { std::cout << std::setprecision(6) << std::setw(8) << x << " = { " << std::hex << std::uppercase << std::setfill('0'); for (auto const b : bytes) std::cout << std::setw(2) << std::to_integer<int>(b) << ' '; std::cout << std::dec << "}\n"; } int main() { /* mutable */ float data[1]{3.141592f}; auto const const_bytes = std::as_bytes(std::span{data}); print(data[0], const_bytes); auto const writable_bytes = std::as_writable_bytes(std::span{data}); // Change the sign bit that is the MSB (IEEE 754 Floating-Point Standard). writable_bytes[3] |= std::byte{0B1000'0000}; print(data[0], const_bytes); }
Possible output:
3.14159 = { D8 0F 49 40 }
-3.14159 = { D8 0F 49 C0 }[edit] See also
| implicitly creates objects in given storage with the object representation reused (function template) | |
| (C++17) |
the byte type (enum) |
