basic_stringbuf(3C++)

Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

NAME

basic_stringbuf

- Associates the input or output sequence with a sequence of arbitrary characters.

SYNOPSIS

#include <sstream>
template<class charT, class traits = char_traits<charT>,

class Allocator = allocator<charT> >

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<charT> >

class basic_stringbuf
: public basic_streambuf<charT, traits> {

public:

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;

typedef basic_ios<charT, traits> ios_type;
typedef basic_string<charT, traits,

Allocator> string_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 underflow();
virtual int_type pbackfail(int_type c = traits::eof());
virtual int_type overflow(int_type c = traits::eof());
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, initializes the input sequence to point to the first character of the buffer. If the opening mode is out, it initializes the output sequence to point to the first character of the buffer. If the opening mode is out | app, it initializes the output sequence to point to the last character of the buffer.

DESTRUCTORS

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 function 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);

A stringbuf maintains an underlying character array for storing buffered characters. This function gives you a way to resize or replace that buffer, with certain restrictions.

First of all, n must be greater than the number of characters currently in the buffer. If n is too small, then setbuf has no effect and returns a null pointer to indicate failure.

If n is large enough, then this function has one of two effects:

-If s is not a null pointer, then setbuf copies the buffered contents of the stringbuf into the n character array starting at s and installs s as the underlying character array used by the stringbuf. s replaces the old underlying array. In this case, the function returns s on success or a null pointer to indicate failure.

Note that the stringbuf now owns s and deletes it if a subsequent call to setbuf replaces it or, failing that, when the stringbuf is destroyed. A program should not itself delete a pointer passed to setbuf if the call succeeds. And s must have been allocated from the heap using new.

-If s is a null pointer, then setbuf resizes the underlying character array to n characters. The function returns a pointer to the beginning of the resized array if the operation is successful, or a null pointer if not.

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 to the first character of the buffer. If the opening mode is out, the function initializes the output sequence to point to the first character of the buffer. If the opening mode is out | app, it initializes the output sequence to point to 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.

EXAMPLE

// 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 to by in_2 to the one
// pointed to 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;

}

STANDARDS CONFORMANCE

ANSI X3J16/ISO WG21 Joint C++ Committee

Rogue Wave Software — Last change: 02 Apr 1998

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Related Articles

basic_stringbuf(3C++)

NAME

SYNOPSIS

DESCRIPTION

INTERFACE

TYPES

CONSTRUCTORS

DESTRUCTORS

MEMBER FUNCTIONS

EXAMPLE

SEE ALSO

STANDARDS CONFORMANCE