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std::basic_ispanstream<CharT,Traits>::span

From cppreference.com
 
 
 
std::basic_ispanstream
Member functions
Underlying buffer operations
basic_ispanstream::span
(C++23)
Non-member functions
 
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 >
void span( SpanLike&& r ) noexcept;
(3) (since C++23)
1) Gets a span referencing the written area if std::ios_base::out is set in the open mode of the wrapped std::basic_spanbuf, or a span referencing the underlying buffer otherwise.
2) Makes the wrapped std::basic_spanbuf perform I/O on the buffer referenced by s.
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.

Contents

[edit] Parameters

s - std::span referencing the storage to be use as the new underlying buffer of stream
r - borrowed_range to be use as the new underlying buffer of stream

[edit] 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)

[edit] Example

#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);
}

Output:

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

[edit] See also

(C++23)
obtains or initializes an underlying buffer according to mode
(public member function of std::basic_spanbuf<CharT,Traits>) [edit]