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Gnafu
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 Posted: Mon Jun 19, 2006 4:05 pm Post subject: how to insert tow byte in front of a file |
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(Hi to all... ^_^)
I tryed theese ways:
fstream riaperto( "codici.dat", ios::out|ios::binary|ios::app);
if(riaperto.bad()){
cerr<<"errore di apertura"<<endl;
system("Pause");
}
riaperto.seekp(ios::beg);
riaperto.put(char(nbyte/256));
riaperto.put(char(nbyte%256));
^= This one writes the bytes at the end of the file (allright, it's the
"app") .
ofstream riaperto( "codici.dat", ios::out|ios::binary);
if(riaperto.bad()){
cerr<<"errore di apertura"<<endl;
system("Pause");
}
riaperto.seekp(ios::beg);
riaperto.put(char(nbyte/256));
riaperto.put(char(nbyte%256));
This one it writes at the beginning but, then, the file contains only that
tow bytes... (overwrite)
What can i do?
Thanks in advance..
Gnafu
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Ralf Fassel
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| Posted: Mon Jun 19, 2006 6:57 pm Post subject: Re: how to insert tow byte in front of a file |
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* "Gnafu" <chiedimela (AT) in (DOT) news.ciaociao>
| This one it writes at the beginning but, then, the file contains
| only that tow bytes... (overwrite)
|
| What can i do?
See
http://www.faqs.org/faqs/C-faq/faq/
In there, topics
12.30 I'm trying to update a file in place, by using fopen mode "r+",
reading a certain string, and writing back a modified string,
but it's not working.
and
19.14 How can I insert or delete a line (or record) in the middle of a
file?
R'
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kanze
Guest
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| Posted: Tue Jun 20, 2006 6:44 pm Post subject: Re: how to insert tow byte in front of a file |
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Gnafu wrote:
To start with, what's a "tow byte"? And what are you really
trying to do: insert an additional byte at the start of the
file, or replace the existing byte.
| Quote: | I tryed theese ways:
fstream riaperto( "codici.dat", ios::out|ios::binary|ios::app);
if(riaperto.bad()){
cerr<<"errore di apertura"<<endl;
system("Pause");
}
riaperto.seekp(ios::beg);
riaperto.put(char(nbyte/256));
riaperto.put(char(nbyte%256));
^= This one writes the bytes at the end of the file (allright,
it's the "app") .
|
That's the definition of ios::app---all writes go to the end of
file. (Atomically, if possible.)
| Quote: | ofstream riaperto( "codici.dat", ios::out|ios::binary);
|
This truncates the file.
| Quote: | if(riaperto.bad()){
cerr<<"errore di apertura"<<endl;
system("Pause");
}
riaperto.seekp(ios::beg);
riaperto.put(char(nbyte/256));
riaperto.put(char(nbyte%256));
This one it writes at the beginning but, then, the file
contains only that tow bytes... (overwrite)
What can i do?
|
What do you want to do? To overwrite bytes in a file, you need
to open it for bidirectional access: ios::in|ios::out. If you
want to insert bytes, however, you can't without copying the
entire file.
--
James Kanze GABI Software
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
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