cppdraft_translate/cppdraft/spanbuf/virtuals.md

[spanbuf.virtuals]

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 andios_base​::​in is not set in mode,

• (4.3.2)

buf.size() otherwise.

5

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If baseoff+off would overflow, or if baseoff+off is less than zero, or if baseoff+off is greater than buf.size(), the positioning operation fails.

Otherwise, the function computesoff_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(s, n));return this;