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/sys$common/syshlp/helplib.hlb CXXLSTD, IOStreams, strstreambuf *Conan The Librarian |
Standard C++ Library
Copyright 1996, Rogue Wave Software, Inc.
NAME
strstreambuf
This page describes the ANSI strstreambuf class. If you would like
information on the pre-ANSI strstreambuf class, use the command:
help cxxl
SYNOPSIS
#include <strstream>
class strstreambuf
: public basic_streambuf<char>
DESCRIPTION
The class strstreambuf is derived from basic_streambuf specialized
on type char to associate possibly the input sequence and
possibly the output sequence with a tiny character array, whose
elements store arbitrary values.
Each object of type strstreambuf 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 means that you can read and write characters at
different positions in objects of type strstreambuf without any
conflict (in opposition to the basic_filebuf objects).
The underlying array has several attributes:
+ allocated, set when a dynamic array has been allocated, and
hence should be freed by the destructor of the strstreambuf
object.
+ constant, set when the array has const elements, so the output
sequence cannot be written.
+ dynamic, set when the array object is allocated
(or reallocated) as necessary to hold a character sequence that
can change in length.
+ frozen, set when the program has requested that the array will
not be altered, reallocated, or freed.
INTERFACE
class strstreambuf
: public basic_streambuf<char> {
public:
typedef char_traits<char> traits;
typedef basic_ios<char, traits> ios_type;
typedef char char_type;
typedef typename traits::int_type int_type;
typedef typename traits::pos_type pos_type;
typedef typename traits::off_type off_type;
explicit strstreambuf(streamsize alsize = 0);
strstreambuf(void *(*palloc)(size_t), void (*pfree)(void *));
strstreambuf(char *gnext, streamsize n, char *pbeg = 0);
strstreambuf(unsigned char *gnext, streamsize n,
unsigned char *pbeg = 0);
strstreambuf(signed char *gnext, streamsize n,
signed char *pbeg = 0);
strstreambuf(const char *gnext, streamsize n);
strstreambuf(const unsigned char *gnext, streamsize n);
strstreambuf(const signed char *gnext, streamsize n);
virtual ~strstreambuf();
void freeze(bool f = 1);
char *str();
int pcount() const;
protected:
virtual int_type overflow(int_type c = traits::eof());
virtual int_type pbackfail(int_type c = traits::eof());
virtual int_type underflow();
virtual pos_type seekoff(off_type, ios_type::seekdir way,
ios_type::openmode which =
ios_type::in | ios_type::out);
virtual pos_type seekpos(pos_type sp, ios_type::openmode which =
ios_type::in | ios_type::out);
virtual streambuf* setbuf(char *s, streamsize n);
virtual streamsize xsputn(const char_type* s, streamsize n);
};
TYPES
char_type
The type char_type is a synonym of type char.
int_type
The type int_type is a synonym of type traits::in_type.
ios_type
The type ios_type is an instantiation of class basic_ios on type char.
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.
traits
The type traits is a synonym of type char_traits<char>.
CONSTRUCTORS
explicit strstreambuf(streamsize alsize = 0);
Constructs an object of class strstreambuf, initializing the base
class with streambuf(). After initialization the strstreambuf
object is in dynamic mode and its array object has a size of
alsize.
strstreambuf(void* (*palloc)(size_t),
void (*pfree)(void*));
Constructs an object of class strstreambuf, initializing the base
class with streambuf(). After initialization the strstreambuf
object is in dynamic mode. The function used to allocate memory
is pointed at by void* (*palloc)(size_t) and the one used to
free memory is pointed at by void (*pfree)(void*).
strstreambuf(char* gnext, streamsize n,
char* pbeg = 0);
strstreambuf(signed char* gnext, streamsize n,
signed char* pbeg = 0);
strstreambuf(unsigned char* gnext, streamsize n,
unsigned char* pbeg = 0);
Constructs an object of class strstreambuf, initializing the base
class with streambuf(). The argument gnext point to the first
element of an array object whose number of elements is:
n, if n > 0
::strlen(gnext), if n == 0
INT_MAX, if n < 0
If pbeg is a null pointer set only the input sequence
to gnext, otherwise set also the output sequence to
pbeg.
strstreambuf(const char* gnext, streamsize n);
strstreambuf(const signed char* gnext, streamsize n);
strstreambuf(const unsigned char* gnext, streamsize n);
Constructs an object of class strstreambuf, initializing the base
class with streambuf(). The argument gnext point to the first
element of an array object whose number of elements is:
n, if n > 0
::strlen(gnext), if n == 0
INT_MAX, if n < 0
Set the input sequence to gnext and the mode to constant.
DESTRUCTORS
virtual ~strstreambuf();
Destroys an object of class strstreambuf. The function frees the
dynamically allocated array object only if allocated is set and
frozen is not set.
MEMBER FUNCTIONS
void
freeze(bool freezefl = 1);
If the mode is dynamic, alters the freeze status of the dynamic
array as follows:
+ If freezefl is false, the function sets the freeze status
to frozen.
+ Otherwise, it clears the freeze status.
int_type
overflow( int_type c = traits::eof() );
If the output sequence has a put position available, and c is not
traits::eof(), then write c into it. If there is no position
available, the function grow the size of the array object by
allocating more memory and then write c at the new current put
position. If dynamic is not set or if frozen is set the operation
fails. The function returns traits::not_eof(c), except if it
fails, in which case it returns traits::eof().
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, move
the input sequence one position backward. If the operation
fails, the function returns traits::eof(). Otherwise it returns
traits::not_eof(c).
int
pcount() const;
Returns the size of the output sequence.
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, alters the stream position
of both the input and the output sequence. If the open
mode is in, alters the stream position of only the
input sequence, and if it is out, alters the stream
position of only the output sequence. The new position is
calculated by combining the two parameters off (dis-
placement) 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, alters the stream position
of both the input and the output sequence. If the open
mode is in, alters the stream position of only the
input sequence, and if it is out, alters the stream
position of only the output sequence. 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.
strstreambuf*
setbuf(char* s, streamsize n);
If dynamic is set and freeze is not, proceed as follows:
If s is not a null pointer and n is greater than the number of
characters already in the current array, replaces it (copy its
contents) by the array of size n pointed at by s.
char*
str();
Calls freeze(), then returns the beginning pointer for the input
sequence.
int_type
underflow();
If the input sequence has a read position available, returns the
content of this position. Otherwise 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.
In the case where s is a null pointer and n is greater than the
number of characters already in the current array, resize it to
size n.
If the function fails, it returns a null pointer.
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/strstreambuf.cpp
//
#include<iostream>
#include<strstream>
#include<iomanip>
void main ( )
{
using namespace std;
// create a read/write strstream object
// and attach it to an ostrstream object
ostrstream out;
// tie the istream object to the ostrstream object
istream in(out.rdbuf());
// output to out
out << "anticonstitutionellement is a big word !!!";
// create a NTBS
char *p ="Le rat des villes et le rat des champs";
// output the NTBS
out << p << endl;
// resize the buffer
if ( out.rdbuf()->pubsetbuf(0,5000) )
cout << endl << "Success in allocating the buffer" << endl;
// output the all buffer to stdout
cout << in.rdbuf( );
// output the decimal conversion of 100 in hex
// with right padding and a width field of 200
out << dec << setfill('!') << setw(200) << 0x100 << endl;
// output the content of the input sequence to stdout
cout << in.rdbuf( ) << endl;
// number of elements in the output sequence
cout << out.rdbuf()->pcount() << endl;
// resize the buffer to a minimum size
if ( out.rdbuf()->pubsetbuf(0,out.rdbuf()->pcount()) )
cout << endl << "Success in resizing the buffer" << endl;
// output the content of the all array object
cout << out.rdbuf()->str() << endl;
}
SEE ALSO
char_traits, ios_base, basic_ios,
basic_streambuf, istrstream(3c++), ostrstream,
strstream(3c++)
Working Paper for Draft Proposed International Standard for
Information Systems--Programming Language C++, Annex D
Compatibility features Section D.5
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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