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VMS Help CXXLSTD, string, basic_stringbuf *Conan The Librarian |
Standard C++ Library
Copyright 1996, Rogue Wave Software, Inc.
NAME
basic_stringbuf
SYNOPSIS
#include <sstream>
template<class charT, class traits = char_traits<charT>,
class Allocator = allocator<void> >
class basic_stringbuf
: public basic_streambuf<charT, traits>
DESCRIPTION
The class basic_stringbuf is derived from basic_streambuf. Its
purpose is to associate the input or output sequence with a sequence
of arbitrary characters. The sequence can be initialized from,
or made available as, an object of class basic_string. Each
object of type basic_stringbuf<charT,traits,Allocator> controls two
character sequences:
+ A character input sequence;
+ A character output sequence.
Note: see basic_streambuf.
The two sequences are related to each other, but are manipulated
separately. This allows you to read and write characters at
different positions in objects of type basic_stringbuf
without any conflict (as opposed to the basic_filebuf objects,
in which a joint file position is maintained).
INTERFACE
template<class charT, class traits = char_traits<charT>,
class allocator<void> >
class basic_stringbuf
: public basic_streambuf<charT, traits> {
public:
typedef basic_ios<charT, traits> ios_type;
typedef basic_string<charT, traits,
Allocator> string_type;
typedef charT char_type;
typedef typename traits::int_type int_type;
typedef typename traits::pos_type pos_type;
typedef typename traits::off_type off_type;
explicit basic_stringbuf(ios_base::openmode which =
(ios_base::in | ios_base::out));
explicit basic_stringbuf(const string_type& str,
ios_base::openmode which =
(ios_base::in | ios_base::out));
virtual ~basic_stringbuf();
string_type str() const;
void str(const string_type& str_arg);
protected:
virtual int_type overflow(int_type c = traits::eof());
virtual int_type pbackfail(int_type c = traits::eof());
virtual int_type underflow();
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 streamsize xsputn(const char_type* s, streamsize n);
};
TYPES
char_type
The type char_type is a synonym for the template parameter charT.
ios_type
The type ios_type is an instantiation of class basic_ios on type
charT.
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.
string_type
The type string_type is an instantiation of class basic_string on
type charT.
stringbuf
The type stringbuf is an instantiation of class basic_stringbuf on
type char:
typedef basic_stringbuf<char> stringbuf;
traits_type
The type traits_type is a synonym for the template parameter traits.
wstringbuf
The type wstringbuf is an instantiation of class basic_stringbuf on
type wchar_t:
typedef basic_stringbuf<wchar_t> wstringbuf;
CONSTRUCTORS
explicit basic_stringbuf(ios_base::openmode which =
ios_base::in | ios_base::out);
Constructs an object of class basic_stringbuf,
initializing the base class with
basic_streambuf(), and initializing the open mode
with which.
explicit basic_stringbuf(const string_type& str,
ios_base::openmode which =
ios_base::in | ios_base::out);
Constructs an object of class basic_stringbuf,
initializing the base class with
basic_streambuf(), and initializing the open mode
with which. The string object str is
copied to the underlying buffer. If the opening
mode is in, initialize the input sequence to point
at the first character of the buffer. If the
opening mode is out, it initializes the output
sequence to point at the first
character of the buffer. If the opening mode is
out | app, it initializes the output sequence
to point at the last character of the buffer.
DESTRUCTOR
virtual ~basic_stringbuf();
Destroys an object of class basic_stringbuf.
MEMBER FUNCTIONS
int_type
overflow(int_type c = traits::eof() );
If the output sequence has a put position available, and c is not
traits::eof(), then this functions writes c into it. If there is
no position available, the function increases the size of the
buffer by allocating more memory and then writes c at the
new current put position. If the operation fails, the function
returns traits::eof(). Otherwise it returns traits::not_eof(c).
int_type
pbackfail( int_type c = traits::eof() );
Puts back the character designated by c into the input sequence. If
traits::eq_int_type(c,traits::eof()) returns true, the function
moves the input sequence one position backward. If the operation
fails, the function returns traits::eof(). Otherwise it returns
traits::not_eof(c).
pos_type
seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which =
ios_base::in | ios_base::out);
If the open mode is in | out, this function alters the
stream position of both the input and the output sequences.
If the open mode is in, it alters the stream
position of only the input sequence, and if it is out,
it alters the stream position of the output sequence. The
new position is calculated by combining the two parameters
off (displacement) and way (reference point). If the
current position of the sequence is invalid before
repositioning, the operation fails and the return value is
pos_type(off_type(-1)). Otherwise the function returns the
current new position.
pos_type
seekpos(pos_type sp,ios_base::openmode which =
ios_base::in | ios_base::out);
If the open mode is in | out, seekpos() alters the stream
position of both the input and the output sequences. If
the open mode is in, it alters the stream position of the
input sequence only, and if the open mode is out, it
alters the stream position of the output sequence only. If
the current position of the sequence is invalid before
repositioning, the operation fails and the return
value is pos_type(off_type(-1)). Otherwise the function
returns the current new position.
basic_streambuf<charT,traits>*
setbuf(char_type*s, streamsize n);
If the string buffer object is opened in output mode, proceed
as follows:
if s is not a null pointer and n is greater than the content of
the current buffer, replace it (copy its contents) by the buffer
of size n pointed at by s. In the case where s is a null
pointer and n is greater than the content of the current
buffer, resize it to size n. If the function fails, it returns
a null pointer.
string_type
str() const;
Returns a string object of type string_type whose content is a copy
of the underlying buffer contents.
void
str(const string_type& str_arg);
Clears the underlying buffer and copies the string object str_arg
into it. If the opening mode is in, initializes the input
sequence to point at the first character of the buffer. If
the opening mode is out, the function initializes the output
sequence to point at the first character of the buffer. If
the opening mode is out | app, it initializes the out-
put sequence to point at the last character of the buffer.
int_type
underflow();
If the input sequence has a read position available, the function
returns the contents of this position. Otherwise it tries to expand
the input sequence to match the output sequence and if possible
returns the content of the new current position. The function
returns traits::eof() to indicate failure.
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. The function returns the number
of characters written.
EXAMPLES
//
// stdlib/examples/manual/stringbuf.cpp
//
#include<iostream>
#include<sstream>
#include<string>
void main ( )
{
using namespace std;
// create a read/write string-stream object on tiny char
// and attach it to an ostringstream object
ostringstream out_1(ios_base::in | ios_base::out);
// tie the istream object to the ostringstream object
istream in_1(out_1.rdbuf());
// output to out_1
out_1 << "Here is the first output";
// create a string object on tiny char
string string_ex("l'heure est grave !");
// open a read only string-stream object on tiny char
// and initialize it
istringstream in_2(string_ex);
// output in_1 to the standard output
cout << in_1.str() << endl;
// output in_2 to the standard output
cout << in_2.rdbuf() << endl;
// reposition in_2 at the beginning
in_2.seekg(0);
stringbuf::pos_type pos;
// get the current put position
// equivalent to
// out_1.tellp();
pos = out_1.rdbuf()->pubseekoff(0,ios_base::cur,
ios_base::out);
// append the content of stringbuffer
// pointed at by in_2 to the one
// pointed at by out_1
out_1 << ' ' << in_2.rdbuf();
// output in_1 to the standard output
cout << in_1.str() << endl;
// position the get sequence
// equivalent to
// in_1.seekg(pos);
in_1.rdbuf()->pubseekpos(pos, ios_base::in);
// output "l'heure est grave !"
cout << in_1.rdbuf() << endl << endl;
}
SEE ALSO
char_traits, ios_base, basic_ios,
basic_streambuf, basic_string,
basic_istringstream, basic_ostringstream,
basic_stringstream
Working Paper for Draft Proposed International Standard for Information
Systems--Programming Language C++, Section 27.7.1
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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