31 Input/output library [input.output]

31.9 Span-based streams [span.streams]

31.9.3 Class template basic_spanbuf [spanbuf]

31.9.3.5 Overridden virtual functions [spanbuf.virtuals]

1
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[Note 1: 
Because the underlying buffer is of fixed size, neither overflow, underflow, nor pbackfail can provide useful behavior.
— end note]
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pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override;
2
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Effects: Alters the stream position within one or both of the controlled sequences, if possible, as follows:
  • (2.1)
    If ios_base​::​in is set in which, positions the input sequence; xnext is gptr(), xbeg is eback().
  • (2.2)
    If ios_base​::​out is set in which, positions the output sequence; xnext is pptr(), xbeg is pbase().
3
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If both ios_base​::​in and ios_base​::​out are set in which and way is ios_base​::​cur, the positioning operation fails.
4
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For a sequence to be positioned, if its next pointer xnext (either gptr() or pptr()) is a null pointer and the new offset newoff as computed below is nonzero, the positioning operation fails.
Otherwise, the function determines baseoff as a value of type off_type as follows:
  • (4.1)
    0 when way is ios_base​::​beg;
  • (4.2)
    (pptr() - pbase()) for the output sequence, or (gptr() - eback()) for the input sequence when way is ios_base​::​cur;
  • (4.3)
    when way is ios_base​::​end :
    • (4.3.1)
      (pptr() - pbase()) if ios_base​::​out is set in mode and ios_base​::​in is not set in mode,
    • (4.3.2)
      buf.size() otherwise.
5
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If would overflow, or if is less than zero, or if is greater than buf.size(), the positioning operation fails.
Otherwise, the function computes off_type newoff = baseoff + off; and assigns xbeg + newoff to the next pointer xnext.
6
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Returns: pos_type(off_type(-1)) if the positioning operation fails; pos_type(newoff) otherwise.
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pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
7
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Effects: Equivalent to: return seekoff(off_type(sp), ios_base::beg, which);
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basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n) override;
8
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Effects: Equivalent to: this->span(std::span<charT>(s, n)); return this;