NAME¶

std::as_bytes,std::as_writable_bytes - std::as_bytes,std::as_writable_bytes

Synopsis¶

Defined in header <span>
template< class T, std::size_t N >

std::span<const std::byte, S/* see below */> (1) (since C++20)

as_bytes( std::span<T, N> s ) noexcept;
template< class T, std::size_t N >

std::span<std::byte, S/* see below */> (2) (since C++20)

as_writable_bytes( std::span<T, N> s ) noexcept;

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.

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()}.

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 }

See also¶

start_lifetime_as implicitly creates objects in given storage with the object
start_lifetime_as_array representation reused
(C++23) (function template)
byte the byte type
(C++17) (enum)