Library: Input/output
basic_stringbufbasic_streambuf
|
basic_stringbuf() char_type ios_type off_type |
overflow() pbackfail() pos_type seekoff() |
seekpos() setbuf() str() traits_type |
underflow() xsputn() |
Class that associates the input or output sequence with a sequence of arbitrary characters
#include <sstream>
namespace std {
template<class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT> >
class basic_stringbuf;
}
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 controls two character sequences:
a character input sequence
a character output sequence
See basic_streambuf for more information.
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).
namespace std {
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;
explicit basic_stringbuf(ios_base::openmode =
(ios_base::in | ios_base::out));
explicit basic_stringbuf(const basic_string<char_type,
traits_type, Allocator>&,
ios_base::openmode =
ios_base::in | ios_base::out);
basic_string<char_type, traits_type, Allocator> str() const;
void str(const basic_string<char_type, traits_type, Allocator>&);
protected:
virtual int_type underflow();
virtual int_type pbackfail(int_type = traits::eof());
virtual int_type overflow(int_type = traits::eof());
virtual basic_streambuf<char_type, traits_type>*
setbuf(char_type*,streamsize);
virtual pos_type seekoff(off_type, ios_base::seekdir,
ios_base::openmode = ios_base::in | ios_base::out);
virtual pos_type seekpos(pos_type,
ios_base::openmode = ios_base::in | ios_base::out);
virtual streamsize xsputn(const char_type*, streamsize);
};
}
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.
traits_type
The type traits_type is a synonym for the template parameter traits.
stringbuf
The type stringbuf is a specialization of class template basic_stringbuf on type char:
typedef basic_stringbuf<char> stringbuf;
wstringbuf
The type wstringbuf is a specialization of class template basic_stringbuf on type wchar_t:
typedef basic_stringbuf<wchar_t> wstringbuf;
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, initializes the output sequence to point to the first character of the buffer.
If the opening mode is out | app, initializes the output sequence to point to the last character of the buffer.
int_type overflow(int_type c = traits_type::eof());
If the output sequence has a put position available, and c is not traits_type::eof(), 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_type::eof(). Otherwise, it returns traits_type::not_eof(c).
int_type pbackfail(int_type c = traits_type::eof());
Puts back the character designated by c into the input sequence. If traits_type::eq_int_type(c,traits_type::eof()) returns true, the function moves the input sequence one position backward. If the operation fails, the function returns traits_type::eof(). Otherwise, it returns traits_type::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 only 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, the 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 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, this function has one of the following effects:
If s is not a null pointer, 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 on failure. The caller is responsible for deleting the buffer.
If s is a null pointer and n is 0, the function has no effect.
If s is a null pointer, 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. The object is responsible for deleting the buffer.
basic_string<char_type, traits_type, Allocator> str() const;
Returns a string object of type basic_string<char_type, traits_type, Allocator>, whose content is a copy of the underlying buffer contents.
void str(const basic_string<char_type, traits_type, Allocator>& str);
Clears the underlying buffer and copies the string object str 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, 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, traits_type::to_int_type(*gptr()). The function returns traits_type::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.
//
// stringbuf.cpp
//
#include <iostream> // for cout, endl
#include <sstream> // for istringstream, ostringstream
#include <string> // for string
int main ()
{
// create a read/write string-stream object on tiny char
// and attach it to an ostringstream object
std::ostringstream out_1 (std::ios::in | std::ios::out);
// tie the istream object to the ostringstream object
std::istream in_1 (out_1.rdbuf ());
// output to out_1
out_1 << "Here is the first ouput";
// create a string object on tiny char
std::string string_ex = "L'heure est grave!";
// open a read only stringstream object and initialize it
std::istringstream in_2 (string_ex);
// output in_1 to the standard output
std::cout << in_1.rdbuf () << std::endl;
// reposition in_1 at the beginning
in_1.seekg (0);
// output in_2 to the standard output
std::cout << in_2.rdbuf () << std::endl;
// reposition in_2 at the beginning
in_2.seekg (0);
// get the current put position (equivalent to
// out_1.tellp())
std::stringbuf::pos_type pos =
out_1.rdbuf ()->pubseekoff (0, std::ios::cur,
std::ios::out);
// append the content of the stringbuf pointed to by in_2
// to the one pointed at by out_1
out_1 << ' ' << in_2.rdbuf ();
// output in_1 to the standard output
std::cout << in_1.rdbuf () << std::endl;
// position the get sequence (equivalent to
// in_1.seekg (pos))
in_1.rdbuf ()->pubseekpos (pos, std::ios::in);
// output "L'heure est grave!"
std::cout << in_1.rdbuf () << std::endl;
return 0;
}
Program Output:
Here is the first ouput L'heure est grave! Here is the first ouput L'heure est grave! L'heure est grave!
char_traits, ios_base, basic_ios, basic_streambuf, basic_string, basic_istringstream, basic_ostringstream, basic_stringstream
ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 27.7.1