std::basic_ospanstream::span(3)

NAME
std::basic_ospanstream::span - std::basic_ospanstream::span

Synopsis
   std::span<CharT> span() const noexcept; (1) (since C++23)
   void span( std::span<CharT> s ) noexcept; (2) (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.

Parameters
   s - std::span referencing the storage 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) (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
   span obtains or initializes an underlying buffer according to mode
   (C++23) (public member function of std::basic_spanbuf<CharT,Traits>)