std::basic_...tream::span(3)

✨ std::basic_...tream::span(3) ✨

okay so we’re in the C++ Standard Libary manual, bestie — yes, that spelling is literally on the page, don’t come for me 💀. This one is all about std::basic_ispanstream::span, and the page title is std::basic_...tream::span(3), so we’re keeping both exactly as printed 🫶.

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🌸 NAME 🌸

std::basic_ispanstream::span — std::basic_ispanstream::span

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🦋 Synopsis 🦋

std::span<const CharT> span() const noexcept; (1) (since C++23)
void span( std::span<CharT> s ) noexcept;     (2) (since C++23)
template< class SpanLike >                    (3) (since C++23)
void span( SpanLike&& r ) noexcept;

1. Gets a std::span referencing the written area if std::ios_base::out is set in the open mode of the wrapped std::basic_spanbuf, or a std::span referencing the underlying buffer otherwise. it’s giving “depends on the mode” energy 💅
2. Makes the wrapped std::basic_spanbuf perform I/O on the buffer referenced by s. iconic little rebuffer move ✨
3. Same as (2), except that s is obtained as if by:

std::span<const CharT> cs{std::forward<SpanLike>(r)};
std::span<CharT> s{const_cast<CharT*>(cs.data()), cs.size()};

This overload participates in overload resolution only if SpanLike models borrowed_range, std::convertible_to<SpanLike, std::span<CharT>> is false, and std::convertible_to<SpanLike, std::span<const CharT>> is true. very “only if the vibes are exactly right” of it 🎀

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🎀 Parameters 🎀

• s — std::span referencing the storage to be used as the new underlying buffer of stream.
• r — borrowed_range to be used as the new underlying buffer of stream.

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💖 Return value 💖

1. A std::span referencing the underlying buffer or written area, depending on the open mode of the wrapped std::basic_spanbuf. 2,3) (none)

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🌈 Example 🌈

Run this code, bestie — it’s a whole little spanstream story:

#include <cassert>
#include <iostream>
#include <span>
#include <spanstream>

int main()
{
    char out_buf[16];
    std::ospanstream ost{std::span<char>{out_buf}};
    ost << "C++" << ' ' << 23 << '\0'; // note explicit null-termination
    auto sp = ost.span();
    assert(
        sp[0] == 'C' && sp[1] == '+' && sp[2] == '+' &&
        sp[3] == ' ' && sp[4] == '2' && sp[5] == '3' &&
        sp[6] == '\0'
    );
    std::cout << "sp.data(): [" << sp.data() << "]\n";
    std::cout << "out_buf: [" << out_buf << "]\n";
    // spanstream uses out_buf as internal storage, no allocations
    assert(static_cast<char*>(out_buf) == sp.data());

    const char in_buf[] = "X Y 42";
    std::ispanstream ist{std::span<const char>{in_buf}};
    assert(static_cast<const char*>(in_buf) == ist.span().data());
    char c;
    ist >> c;
    assert(c == 'X');
    ist >> c;
    assert(c == 'Y');
    int i;
    ist >> i;
    assert(i == 42);
    ist >> i; // buffer is exhausted
    assert(!ist);
}

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🌟 Output: 🌟

sp.data(): [C++ 23]
out_buf: [C++ 23]

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👀 See also 👀

• span — obtains or initializes an underlying buffer according to mode; (C++23) public member function of std::basic_spanbuf<CharT,Traits>

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🫶 footer vibes, exactly as the page closes: http://cppreference.com, 2024.06.10, std::basic_...tream::span(3). That’s the source/version/date trio, bestie — periodt 💅