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

From cppreference.com

C++
Input/output library
std::basic_ispanstream
Member functions
(C++23)
(C++23)
(C++23)
(C++23)
Underlying buffer operations
basic_ispanstream::span
(C++23)
Non-member functions
(C++23)
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 .

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

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)

Example

Run this code 
#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]

See also

obtains or initializes an underlying buffer according to mode
(public member function of std::basic_spanbuf<CharT,Traits> )
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