How to define an global object like cout?

[PengYu.UT]

Hi,

I want to define an unique file object, like cout, where there is the
only such one in the program.

It seems that singleton pattern can be used for this purpose. But I'm
wondering if cout is an singleton. I would guess not. There were some
threads in the newsgroup discuss about cout and singleton, which is
too long for me to catch the main point. Can somebody give me a brief
introduction on this? And show me how to define an global file object?

Thanks,
Peng

[Gianni Mariani]

Pe*******@gmail.com wrote:

Hi,

I want to define an unique file object, like cout, where there is the
only such one in the program.

It seems that singleton pattern can be used for this purpose. But I'm
wondering if cout is an singleton. I would guess not. There were some
threads in the newsgroup discuss about cout and singleton, which is
too long for me to catch the main point. Can somebody give me a brief
introduction on this? And show me how to define an global file object?

.....
// public header file myiostream.h

#include <iostream>

namespace MYSPACE
{
extern std::ostream & MYOSTREAM;
} // end namespace
.....
.....
// implementation file - myiostream.cpp

#include "myiostream.h"
#include <fstream>

namespace { // anon namespace
struct my_fstream : std::fostream
{
std::fostream m_fostream;
my_fstream()
: m_fostream( "file name" );
{
// do whatever you want to open the file before main()
// is called here
}
};

my_fstream s_mostream;

}// end anon namespace

namespace MYSPACE
{
// create object - mostream
std::ostream & MYOSTREAM = s_mostream;
} // end namespace

.....

///// not tested in a compiler - I probably broke somthing but you
///// should get the drift

[Kai-Uwe Bux]

Gianni Mariani wrote:

Pe*******@gmail.com wrote:

>Hi,

I want to define an unique file object, like cout, where there is the
only such one in the program.

It seems that singleton pattern can be used for this purpose. But I'm
wondering if cout is an singleton. I would guess not. There were some
threads in the newsgroup discuss about cout and singleton, which is
too long for me to catch the main point. Can somebody give me a brief
introduction on this? And show me how to define an global file object?

....
// public header file myiostream.h

#include <iostream>

namespace MYSPACE
{
extern std::ostream & MYOSTREAM;
} // end namespace
....
....
// implementation file - myiostream.cpp

#include "myiostream.h"
#include <fstream>

namespace { // anon namespace
struct my_fstream : std::fostream
{
std::fostream m_fostream;
my_fstream()
: m_fostream( "file name" );
{
// do whatever you want to open the file before main()
// is called here
}
};

my_fstream s_mostream;

}// end anon namespace

namespace MYSPACE
{
// create object - mostream
std::ostream & MYOSTREAM = s_mostream;
} // end namespace

....

///// not tested in a compiler - I probably broke somthing but you
///// should get the drift

I have this vague recollection that this will not completely cut it as far
as implementing a resource like std::cin is concerned (the problem being
something along the lines that std::cin can be used in several compilation
units and one cannot decide up front which one shall do the
initialization). I think, there is a trick that goes by the name of Schwarz
counter used in solving the problem. Anyway, I don't remember the details.
Best

Kai-Uwe Bux

[Gianni Mariani]

Kai-Uwe Bux wrote:
....

I have this vague recollection that this will not completely cut it as far
as implementing a resource like std::cin is concerned (the problem being
something along the lines that std::cin can be used in several compilation
units and one cannot decide up front which one shall do the
initialization). I think, there is a trick that goes by the name of Schwarz
counter used in solving the problem. Anyway, I don't remember the details.

modulo the errors in the code (3 at least), the initialization of the
s_mostream object happens somtime before main() is called. If you need
it initialized before main() then you need to make sure it is
initialized using some different mechanism.