Abstract base class for deriving various stream buffers to facilitate control of character sequences.
| Data Types | |
| char_type int_type off_type pos_type |
streambuf traits_type wstreambuf |
#include <streambuf> template<class charT, class traits = char_traits<charT> > class basic_streambuf;
The class template basic_streambuf<charT,traits> serves as an abstract base class for deriving various stream buffers to facilitate control of character sequences such as:
A character input sequence;
A character output sequence.
Each sequence is associated with three pointers (as described below), which, if non-null, all point into the same charT array object. The array object represents, at any moment, a segment of characters from the sequence. Operations performed on a sequence alter the values pointed to by 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 segment to sequence 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 unwriteable;
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.
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 basic_streambuf<charT, traits>*
setbuf(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 int showmanyc();
virtual streamsize xsgetn(char_type *s, streamsize n);
virtual int_type underflow();
virtual int_type uflow();
virtual int_type pbackfail(int_type c = traits::eof());
virtual streamsize xsputn(const char_type *s,
streamsize n);
virtual int_type overflow(int_type c = traits::eof());
virtual int sync();
};
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;
basic_streambuf();
Constructs an object of class basic_streambuf. Initializes all its pointer member objects to null pointers, and initializes the getloc() member function to return the value of locale::locale().
virtual ~basic_streambuf();
Destroys an object of class basic_streambuf.
locale getloc() const;
If pubimbue() has ever been called, returns the last value of loc supplied. Otherwise, it returns the default (global) locale locale::locale() in effect at the time of construction.
streamsize in_avail();
If a read position is available, returns the number of available characters 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 it 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 it 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 it 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 it 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, it 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 it 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.
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 when 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 if it fails 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 a 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 a 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 returns -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 to by gptr(), if gptr() is not null and if gptr() < egptr(). Otherwise the function tries to read character into the buffer. If it fails, it returns 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.
char_traits(3C++), basic_filebuf(3C++), basic_stringbuf(3C++), strstreambuf(3C++)
Working Paper for Draft Proposed International Standard for Information Systems--Programming Language C++, Section 27.5.2
ANSI X3J16/ISO WG21 Joint C++ Committee