streambuf (3C++std) - Tru64 UNIX
Standard C++ LibraryCopyright 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:
man 3C++ streambuf or man streambuf.3C++
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
relationship. 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
position.
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
position.
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
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
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(3C++std), basic_filebuf(3C++std), basic_stringbuf(3C++std),
strstreambuf(3C++std)
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
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