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 */> as_bytes(std::span<T, (1) (since C++20)
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

byte the byte type
(C++17) (enum)