I'm a bit confused about a statement in TC++ST §13.10. It's in reference to
this example:
/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference"
* by Nicolai M. Josuttis, Addison-Wesley, 1999
*
* (C) Copyright Nicolai M. Josuttis 1999.
* Permission to copy, use, modify, sell and distribute this software
* is granted provided this copyright notice appears in all copies.
* This software is provided "as is" without express or implied
* warranty, and with no claim as to its suitability for any purpose.
*/
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
// open file ``example.dat'' for reading and writing
filebuf buffer;
ostream output(&buffer);
istream input(&buffer);
buffer.open ("example.dat", ios::in | ios::out | ios::trunc);
for (int i=1; i<=4; i++) {
// write one line
output << i << ". line" << endl;
// print all file contents
input.seekg(0); // seek to the beginning
char c;
while (input.get(c)) {
cout.put(c);
}
cout << endl;
input.clear(); // clear eofbit and failbit
}
}
He says "Although two different stream objects are used for reading and
writing, the read and write positions are tightly coupled. seekg() and
seekp() call the same member function of the stream buffer.10"
footnote 10 says: "Actually this function can distinguish whether the read
position, the write position, or both positions are to be modified. Only
the standard stream buffers maintain one position for reading and writing."
This is the Doxygen of libstdc++:
http://gcc.gnu.org/onlinedocs/libstd...ce.html#l00967
I'm trying to make heads or tails out of this. If the put pointer and get
pointer are synchronized, then why have two of them? This is what the
std::basic_streambuf pointer declarations look like:
Protected Attributes
locale _M_buf_locale
char_type * _M_in_beg
char_type * _M_in_cur
char_type * _M_in_end
char_type * _M_out_beg
char_type * _M_out_cur
char_type * _M_out_end
--
If our hypothesis is about anything and not about some one or more
particular things, then our deductions constitute mathematics. Thus
mathematics may be defined as the subject in which we never know what we
are talking about, nor whether what we are saying is true.-Bertrand Russell
