27 Input/output library [input.output]

27.8 String-based streams [string.streams]

27.8.2 Class template basic_­stringbuf [stringbuf]

27.8.2.4 Overridden virtual functions [stringbuf.virtuals]

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int_type underflow() override;
1
#
Returns: If the input sequence has a read position available, returns traits​::​to_­int_­type(*gptr()).
Otherwise, returns traits​::​eof().
Any character in the underlying buffer which has been initialized is considered to be part of the input sequence.
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int_type pbackfail(int_type c = traits::eof()) override;
2
#
Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:
  • (2.1)
    If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if the input sequence has a putback position available, and if traits​::​eq(to_­char_­type(c), gptr()[-1]) returns true, assigns gptr() - 1 to gptr().
    Returns: c.
  • (2.2)
    If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if the input sequence has a putback position available, and if mode & ios_­base​::​out is nonzero, assigns c to *--gptr().
    Returns: c.
  • (2.3)
    If traits​::​eq_­int_­type(c, traits​::​eof()) returns true and if the input sequence has a putback position available, assigns gptr() - 1 to gptr().
    Returns: traits​::​not_­eof(c).
3
#
Returns: As specified above, or traits​::​eof() to indicate failure.
4
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Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen.
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int_type overflow(int_type c = traits::eof()) override;
5
#
Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:
  • (5.1)
    If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if either the output sequence has a write position available or the function makes a write position available (as described below), the function calls sputc(c).
    Signals success by returning c.
  • (5.2)
    If traits​::​eq_­int_­type(c, traits​::​eof()) returns true, there is no character to append.
    Signals success by returning a value other than traits​::​eof().
6
#
Remarks: The function can alter the number of write positions available as a result of any call.
7
#
Returns: As specified above, or traits​::​eof() to indicate failure.
8
#
The function can make a write position available only if (mode & ios_­base​::​out) != 0.
To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus at least one additional write position.
If (mode & ios_­base​::​in) != 0, the function alters the read end pointer egptr() to point just past the new write position.
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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;
9
#
Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 113.
Table 113 — seekoff positioning
Conditions
Result
(which & ios_­base​::​in) == ios_­base​::​in
positions the input sequence
(which & ios_­base​::​out) == ios_­base​::​out
positions the output sequence
(which & (ios_­base​::​in |
ios_­base​::​out)) ==
(ios_­base​::​in |
ios_­base​::​out)
and way == either
ios_­base​::​beg or
ios_­base​::​end
positions both the input and the output sequences
Otherwise
the positioning operation fails.
10
#
For a sequence to be positioned, the function determines newoff as indicated in Table 114.
If the sequence's next pointer (either gptr() or pptr()) is a null pointer and newoff is nonzero, the positioning operation fails.
Table 114 — newoff values
Condition
newoff Value
way == ios_­base​::​beg
0
way == ios_­base​::​cur
the next pointer minus the beginning pointer (xnext - xbeg).
way == ios_­base​::​end
the high mark pointer minus the beginning pointer (high_­mark - xbeg).
11
#
If (newoff + off) < 0, or if newoff + off refers to an uninitialized character ([stringbuf.members]), the positioning operation fails.
Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.
12
#
Returns: pos_­type(newoff), constructed from the resultant offset newoff (of type off_­type), that stores the resultant stream position, if possible.
If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_­type(off_­type(-1)).
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pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
13
#
Effects: Equivalent to seekoff(off_­type(sp), ios_­base​::​beg, which).
14
#
Returns: sp to indicate success, or pos_­type(off_­type(-1)) to indicate failure.
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basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n);
15
#
Effects: implementation-defined, except that setbuf(0, 0) has no effect.
16
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Returns: this.