|
VMS Help CXXLSTD, IOStreams, basic_streambuf *Conan The Librarian |
Standard C++ Library
Copyright 1996, Rogue Wave Software, Inc.
NAME
basic_streambuf,streambuf
This page describes the ANSI streambuf class. If you would like
information on the pre-ANSI streambuf class, use the
command:
help cxxl
SYNOPSIS
#include <streambuf>
template<class charT, class traits = char_traits<charT> >
class basic_streambuf;
DESCRIPTION
The class template basic_streambuf<charT,traits> serves as an
abstract base class for deriving various stream buffers whose
objects each control two character sequences:
+ A character input sequence;
+ A character output sequence.
Each sequence is characterized by three pointers which, if non-null,
all point into the same charT array object. The array object
represents, at any moment, a subsequence of characters from the
sequence. Operations performed on a sequence alter the values
stored in these pointers, perform reads and writes directly
to or from associated sequences, and alter "the stream position" and
conversion state as needed to maintain this subsequence rela-
tionship. The three pointers are:
+ The beginning pointer, or lowest element address in the array;
+ The next pointer, or next element address that is a current
candidate for reading or writing;
+ The end pointer, or first element address beyond the end of
the array.
Stream buffers can impose various constraints on the sequences they
control, including:
+ The controlled input sequence may be unreadable;
+ The controlled output sequence may be unwritable;
+ The controlled sequences can be associated with the
contents of other representations for character sequences, such
as external files;
+ The controlled sequences can impose limitations on how the
program can read characters from a sequence, write characters
to a sequence, put characters back into an input sequence,
or alter the stream position.
INTERFACE
template<class charT, class traits = char_traits<charT> >
class basic_streambuf {
public:
typedef charT char_type;
typedef traits traits_type;
typedef typename traits::int_type int_type;
typedef typename traits::pos_type pos_type;
typedef typename traits::off_type off_type;
virtual ~basic_streambuf();
locale pubimbue( const locale& loc);
locale getloc() const;
basic_streambuf<char_type, traits> *
pubsetbuf(char_type *s, streamsize n);
pos_type pubseekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which =
ios_base::in | ios_base::out);
pos_type pubseekpos(pos_type sp, ios_base::openmode which =
ios_base::in | ios_base::out);
int pubsync();
ios_base::openmode which_open_mode();
streamsize in_avail();
int_type snextc();
int_type sbumpc();
int_type sgetc();
streamsize sgetn(char_type *s, streamsize n);
int_type sputbackc(char_type c);
int sungetc();
int_type sputc(char_type c);
streamsize sputn(const char_type *s, streamsize n);
protected:
basic_streambuf();
char_type *eback() const;
char_type *gptr() const;
char_type *egptr() const;
void gbump(int n);
void setg(char_type *gbeg_arg,char_type *gnext_arg,
char_type *gend_arg);
char_type *pbase() const;
char_type *pptr() const;
char_type *epptr() const;
void pbump(int n);
void setp(char_type *pbeg_arg,char_type *pend_arg);
virtual void imbue( const locale& loc);
virtual int_type overflow(int_type c = traits::eof());
virtual int_type pbackfail(int_type c = traits::eof());
virtual int showmanyc();
virtual int_type underflow();
virtual int_type uflow();
virtual streamsize xsgetn(char_type *s, streamsize n);
virtual streamsize xsputn(const char_type *s, streamsize n);
virtual pos_type seekoff(off_type off,ios_base::seekdir way,
ios_base::openmode which =
ios_base::in | ios_base::out);
virtual pos_type seekpos(pos_type sp,ios_base::openmode which =
ios_base::in | ios_base::out);
virtual basic_streambuf<charT, traits>*
setbuf(char_type *s, streamsize n);
virtual int sync();
};
TYPES
char_type
The type char_type is a synonym for the template parameter charT.
int_type
The type int_type is a synonym of type traits::in_type.
off_type
The type off_type is a synonym of type traits::off_type.
pos_type
The type pos_type is a synonym of type traits::pos_type.
streambuf
The type streambuf is an instantiation of class
basic_streambuf on type char:
typedef basic_streambuf<char> streambuf;
traits_type
The type traits_type is a synonym for the template parameter traits.
wstreambuf
The type wstreambuf is an instantiation of class basic_streambuf on
type wchar_t:
typedef basic_streambuf<wchar_t> wstreambuf;
PUBLIC CONSTRUCTOR
basic_streambuf();
Constructs an object of class basic_streambuf and initializes all
its pointer member objects to null pointers and the getloc()
member function to return the value of locale::locale().
PUBLIC DESTRUCTOR
virtual ~basic_streambuf();
Destroys an object of class basic_streambuf.
PUBLIC MEMBER FUNCTIONS
locale
getloc() const;
If pubimbue() has ever been called, returns the last value of loc
supplied, otherwise, the default locale locale::locale() in
effect at the time of construction.
streamsize
in_avail();
If a read position is available, returns the number of available
character in the input sequence. Otherwise calls the protected
function showmanyc().
locale
pubimbue(const locale& loc);
Calls the protected function imbue(loc).
pos_type
pubseekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which =
ios_base::in | ios_base::out );
Calls the protected function seekoff(off,way,which).
pos_type
pubseekpos(pos_type sp, ios_base::openmode which=
ios_base::in | ios_base::out );
Calls the protected function seekpos(sp,which).
basic_streambuf<char_type,traits>*
pubsetbuf(char_type* s,streamsize n);
Calls the protected function setbuf(s,n) .
int
pubsync();
Calls the protected function sync().
int_type
sbumpc();
If the input sequence read position is not available, calls the
function uflow(), otherwise returns *gptr() and increments
the next pointer for the input sequence.
int_type
sgetc();
If the input sequence read position is not available, calls the
protected function underflow(), otherwise returns *gptr() .
streamsize
sgetn(char_type* s, streamsize n);
Calls the protected function xsgetn(s,n).
int_type
snextc();
Calls the function sbumpc() and if it returns traits::eof(),
returns traits::eof(); otherwise calls the function sgetc() .
int_type
sputbackc(char_type c);
If the input sequence putback position is not available, or if
traits::eq(c,gptr() [-1]) returns false, calls the protected
function pbackfail(c), otherwise decrements the next
pointer for the input sequence and returns *gptr().
int_type
sputc(char_type c);
If the output sequence write position is not available, calls the
protected function overflow(traits::to_int_type( c )).
Otherwise, stores c at the next pointer for the output
sequence, increments the pointer, and returns *pptr() .
streamsize
sputn(const char_type* s, streamsize n);
Calls the protected function xsputn(s,n).
int_type
sungetc();
If the input sequence putback position is not available, calls
the protected function pbackfail(). Otherwise decrements
the next pointer for the input sequence and returns *gptr().
ios_base::openmode
which_open_mode();
Returns the mode in which the stream buffer is opened. This
function is not described in the C++ standard.
PROTECTED MEMBER FUNCTIONS
char_type*
eback() const;
Returns the beginning pointer for the input sequence.
char_type*
egptr() const;
Returns the end pointer for the input sequence.
char_type*
epptr() const;
Returns the end pointer for the output sequence.
void
gbump(int n);
Advances the next pointer for the input sequence by n.
char_type*
gptr() const;
Returns the next pointer for the input sequence.
void
imbue(const locale&);
Changes any translations based on locale. The default behavior is
to do nothing, this function has to be overloaded in the
classes derived from basic_streambuf. The purpose of this
function is to allow the derived class to be informed of changes
in locale at the time they occur. The new imbued locale object
is only used by the stream buffer, it does not affect the stream
itself.
int_type
overflow(int_type c = traits::eof() );
The member functions sputc() and sputn() call this function in
case that not enough room can be found in the put buffer to
accommodate the argument character sequence. The function
returns traits::eof() if it fails to make more room
available, or to empty the buffer by writing the characters
to their output device.
int_type
pbackfail(int_type c = traits::eof() );
If c is equal to traits::eof(), gptr() is moved back one position
otherwise c is prepended. The function returns traits::eof() to
indicate failure.
char_type*
pbase() const;
Returns the beginning pointer for the output sequence.
void
pbump(int n);
Advances the next pointer for the output sequence by n.
char_type*
pptr() const;
Returns the next pointer for the output sequence.
pos_type
seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which =
ios_base::in | ios_base::out );
Alters the stream positions within one or more of the controlled
sequences in a way that is defined separately for each class
derived from basic_streambuf. The default behavior is to return
an object of type pos_type that stores an invalid stream posi-
tion.
pos_type
seekpos(pos_type sp, ios_base::openmode which=
ios_base::in | ios_base::out );
Alters the stream positions within one or more of the controlled
sequences in a way that is defined separately for each class
derived from basic_streambuf. The default behavior is to return
an object of class pos_type that stores an invalid stream posi-
tion.
basic_streambuf*
setbuf(char_type* s, streamsize n);
Performs an operation that is defined separately for each class
derived from basic_streambuf. The purpose of this function is to
allow the user to provide his own buffer, or to resize the
current buffer.
void
setg(char_type* gbeg, char_type* gnext, char_type* gend);
Sets up private member for the following to be true:
eback() == gbeg, gptr() == gnext and egptr() == gend
void
setp(char_type* pbeg, char_type* pend);
Sets up private member for the following to be true:
pbase() == pbeg, pptr() == pbeg and epptr() == pend
int
showmanyc();
Returns the number of characters available in the internal
buffer, or -1.
int
sync();
Synchronizes the controlled sequences with the internal buffer,
in a way that is defined separately for each class derived
from basic_streambuf. The default behavior is to do nothing. On
failure the return value is -1.
int_type
underflow();
The public members of basic_streambuf call this function only if
gptr() is null or gptr() >= egptr(). This function returns the
character pointed at by gptr() if gptr() is not null and if
gptr() < egptr(). Otherwise the function try to read
character into the buffer, and if it fails return traits::eof().
int_type
uflow();
Calls underflow() and if underflow() returns traits::eof(),
returns traits::eof(). Otherwise, does gbump(1) and returns the
value of *gptr().
streamsize
xsgetn(char_type* s, streamsize n);
Assigns up to n characters to successive elements of the array
whose first element is designated by s. The characters are read
from the input sequence. Assigning stops when either n
characters have been assigned or a call to sbumpc() would
return traits::eof(). The function returns the number of
characters read.
streamsize
xsputn(const char_type* s, streamsize n);
Writes up to n characters to the output sequence. 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 to sputc() would return
traits::eof(). The function returns the number of characters
written.
SEE ALSO
char_traits, basic_filebuf, basic_stringbuf,
strstreambuf
Working Paper for Draft Proposed International Standard for Information
Systems--Programming Language C++, Section 27.5
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
|
|