[streambuf.virtuals] (original) (raw)

31 Input/output library [input.output]

31.6 Stream buffers [stream.buffers]

31.6.3 Class template basic_streambuf [streambuf]

31.6.3.5 Virtual functions [streambuf.virtuals]

31.6.3.5.1 Locales [streambuf.virt.locales]

void imbue(const locale&);

Effects: Change any translations based on locale.

Remarks: Allows the derived class to be informed of changes in locale at the time they occur.

Between invocations of this function a class derived from streambuf can safely cache results of calls to locale functions and to members of facets so obtained.

Default behavior: Does nothing.

31.6.3.5.2 Buffer management and positioning [streambuf.virt.buffer]

basic_streambuf* setbuf(char_type* s, streamsize n);

Default behavior: Does nothing.

Returnsthis.

pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which= ios_base::in | ios_base::out);

Effects: Alters the stream positions within one or more of the controlled sequences in a way that is defined separately for each class derived frombasic_streambufin this Clause ([stringbuf.virtuals], [filebuf.virtuals]).

Default behavior: Returnspos_type(off_type(-1)).

pos_type seekpos(pos_type sp, ios_base::openmode which= ios_base::in | ios_base::out);

Default behavior: Returnspos_type(off_type(-1)).

Effects: Synchronizes the controlled sequences with the arrays.

That is, ifpbase()is non-null the characters betweenpbase()andpptr()are written to the controlled sequence.

The pointers may then be reset as appropriate.

Returns: -1 on failure.

What constitutes failure is determined by each derived class ([filebuf.virtuals]).

Default behavior: Returns zero.

31.6.3.5.3 Get area [streambuf.virt.get]

streamsize showmanyc();[268](#footnote-268 "The morphemes of showmanyc are “es-how-many-see”, not “show-manic”.")

Returns: An estimate of the number of characters available in the sequence, or .

If it returns a positive value, then successive calls tounderflow()will not returntraits::eof()until at least that number of characters have been extracted from the stream.

Ifshowmanyc()returns , then calls tounderflow()oruflow()will fail.269

Default behavior: Returns zero.

Remarks: Usestraits::eof().

streamsize xsgetn(char_type* s, streamsize n);

Effects: Assigns up to n characters to successive elements of the array whose first element is designated by s.

The characters assigned are read from the input sequence as if by repeated calls tosbumpc().

Assigning stops when either n characters have been assigned or a call tosbumpc()would returntraits::eof().

Returns: The number of characters assigned.270

Remarks: Usestraits::eof().

Thepending sequenceof characters is defined as the concatenation of

the empty sequence if gptr() is null, otherwise the characters in [gptr(), egptr()), followed by
some (possibly empty) sequence of characters read from the input sequence.

Theresult characteris the first character of the pending sequence if it is non-empty, otherwise the next character that would be read from the input sequence.

Thebackup sequenceis the empty sequence if eback() is null, otherwise the characters in [eback(), gptr()).

Effects: The function sets up thegptr()andegptr()such that if the pending sequence is non-empty, thenegptr()is non-null and the characters in [gptr(), egptr()) are the characters in the pending sequence, otherwise either gptr()is null orgptr() == egptr().

Ifeback()andgptr()are non-null then the function is not constrained as to their contents, but the “usual backup condition” is that either

the backup sequence contains at leastgptr() - eback()characters, in which case the characters in [eback(), gptr()) agree with the lastgptr() - eback()characters of the backup sequence, or
the characters in [gptr() - n, gptr()) agree with the backup sequence (where n is the length of the backup sequence).

Returns: traits::to_int_type(c), where c is the first_character_of thepending sequence, without moving the input sequence position past it.

If the pending sequence is null then the function returnstraits::eof()to indicate failure.

Default behavior: Returnstraits::eof().

Remarks: The public members ofbasic_streambufcall this virtual function only ifgptr()is null orgptr() >= egptr().

Preconditions: The constraints are the same as forunderflow(), except that the result character is transferred from the pending sequence to the backup sequence, and the pending sequence is not empty before the transfer.

Default behavior: Callsunderflow().

Ifunderflow()returnstraits::eof(), returnstraits::eof().

Otherwise, returns the value oftraits::to_int_type(*gptr())and increments the value of the next pointer for the input sequence.

Returns: traits::eof()to indicate failure.

31.6.3.5.4 Putback [streambuf.virt.pback]

int_type pbackfail(int_type c = traits::eof());

Thepending sequenceis defined as forunderflow(), with the modifications that

Iftraits::eq_int_type(c, traits::eof())returnstrue, then the input sequence is backed up one character before the pending sequence is determined.
Iftraits::eq_int_type(c, traits::eof())returns false, then c is prepended.
Whether the input sequence is backed up or modified in any other way is unspecified.

Postconditions: On return, the constraints ofgptr(),eback(), andpptr()are the same as forunderflow().

Returns: traits::eof()to indicate failure.

Failure may occur because the input sequence could not be backed up, or if for some other reason the pointers cannot be set consistent with the constraints.

pbackfail()is called only when put back has really failed.

Returns some value other thantraits::eof()to indicate success.

Default behavior: Returnstraits::eof().

Remarks: The public functions ofbasic_streambufcall this virtual function only whengptr()is null,gptr() == eback(), ortraits::eq(traits::to_char_type(c), gptr()[-1])returnsfalse.

Other calls shall also satisfy that constraint.

31.6.3.5.5 Put area [streambuf.virt.put]

streamsize xsputn(const char_type* s, streamsize n);

Effects: Writes up to n characters to the output sequence as if by repeated calls tosputc(c).

The characters written are obtained from successive elements of the array whose first element is designated by s.

Writing stops when either n characters have been written or a call tosputc(c)would returntraits::eof().

It is unspecified whether the function calls overflow() when pptr() == epptr() becomes true or whether it achieves the same effects by other means.

Returns: The number of characters written.

int_type overflow(int_type c = traits::eof());

Effects: Consumes some initial subsequence of the characters of thepending sequence .

The pending sequence is defined as the concatenation of

the empty sequence if pbase() is null, otherwise thepptr() - pbase()characters beginning atpbase(), followed by
the empty sequence iftraits::eq_int_type(c, traits::eof())returnstrue, otherwise the sequence consisting of c.

Preconditions: Every overriding definition of this virtual function obeys the following constraints:

The effect of consuming a character on the associated output sequence is specified.271
Letrbe the number of characters in the pending sequence not consumed.
Ifris nonzero thenpbase()andpptr()are set so that:pptr() - pbase() == rand the r characters starting atpbase()are the associated output stream.
In case r is zero (all characters of the pending sequence have been consumed) then eitherpbase()is set tonullptr, orpbase()andpptr()are both set to the same non-null value.
The function may fail if either appending some character to the associated output stream fails or if it is unable to establishpbase()andpptr()according to the above rules.

Returns: traits::eof()or throws an exception if the function fails.

Otherwise, returns some value other thantraits::eof()to indicate success.272

Default behavior: Returnstraits::eof().

Remarks: The member functionssputc()andsputn()call this function in case that no room can be found in the put buffer enough to accommodate the argument character sequence.