31 Input/output library [input.output]

31.8 String-based streams [string.streams]

31.8.2 Class template basic_stringbuf [stringbuf]

31.8.2.5 Overridden virtual functions [stringbuf.virtuals]

int_type underflow() override;
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.
int_type pbackfail(int_type c = traits::eof()) override;
Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:
  • 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.
  • 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.
  • 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).
Returns: As specified above, or traits​::​eof() to indicate failure.
Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen.
int_type overflow(int_type c = traits::eof()) override;
Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:
  • 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.
  • 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().
Returns: As specified above, or traits​::​eof() to indicate failure.
Remarks: The function can alter the number of write positions available as a result of any call.
The function can make a write position available only if ios_base​::​out is set in mode.
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 ios_base​::​in is set in mode, the function alters the read end pointer egptr() to point just past the new write position.
pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override;
Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 130.
Table 130: seekoff positioning [tab:stringbuf.seekoff.pos]
Conditions
Result
ios_base​::​in is set in which
positions the input sequence
ios_base​::​out is set in which
positions the output sequence
both ios_base​::​in and ios_base​::​out are set in which and either
way == ios_base​::​beg or
way == ios_base​::​end
positions both the input and the output sequences
Otherwise
the positioning operation fails.
For a sequence to be positioned, the function determines newoff as indicated in Table 131.
If the sequence's next pointer (either gptr() or pptr()) is a null pointer and newoff is nonzero, the positioning operation fails.
Table 131: newoff values [tab:stringbuf.seekoff.newoff]
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).
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.
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)).
pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
Effects: Equivalent to seekoff(off_type(sp), ios_base​::​beg, which).
Returns: sp to indicate success, or pos_type(off_type(-1)) to indicate failure.
basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n) override;
Effects: implementation-defined, except that setbuf(0, 0) has no effect.
Returns: this.