how to insert tow byte in front of a file

[Gnafu]

(Hi to all... ^_^)

I tryed theese ways:

fstream riaperto( "codici.dat", ios:ut|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:ut|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

 

[Rolf Magnus]

(Hi to all... ^_^)

I tryed theese ways:

fstream riaperto( "codici.dat", ios:ut|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:ut|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..

Write the new bytes you want to a temporary file, then copy the content of
the original file over. If that was successful, rename the temporary file
to the name of the original.

 

[Jerry Coffin]

[ ... ]

Write the new bytes you want to a temporary file, then copy the content of
the original file over. If that was successful, rename the temporary file
to the name of the original.

....and hope there are no other hard links to the file --
because if there are, you now have two separate files,
and all of the other hard links point to the unmodified
file.

 

[Gnafu]

Write the new bytes you want to a temporary file, then copy the content of

the original file over. If that was successful, rename the temporary file
to the name of the original.

I wanted to not do that....
Ok, thank anyway..

 

[Rolf Magnus]

[ ... ]

Write the new bytes you want to a temporary file, then copy the content
of the original file over. If that was successful, rename the temporary
file to the name of the original.

...and hope there are no other hard links to the file --
because if there are, you now have two separate files,
and all of the other hard links point to the unmodified
file.

That's one of the reasons to better use symlinks ;-)

 

[Alf P. Steinbach]

* Rolf Magnus:

[ ... ]

Write the new bytes you want to a temporary file, then copy the content
of the original file over. If that was successful, rename the temporary
file to the name of the original.

...and hope there are no other hard links to the file --
because if there are, you now have two separate files,
and all of the other hard links point to the unmodified
file.

That's one of the reasons to better use symlinks ;-)

Depends on the OS. Windows supports hardlinks for files, symlinks for
directories, and shortcuts (which are like symlinks but not
automatically resolved) for anything. The rename approach might be
appropriate when safety against file content destruction is important,
you're guaranteed that no other process will create that file in the
span between its deletion and recreation by your program, and efficiency
is valued more than link preservation.

I think it should be a user-selectable option.

Follow-ups to [comp.programming].

 

[hdante]

You'll need to put "POSIX compliant system" on your product
requirements box for doing this:

i = open ("blarg", O_WRONLY);
lseek(i, 0, SEEK_SET);
write(i, my_buffer, 2);
close(i);

 

[Rolf Magnus]

please don't top-post.

u'll need to put "POSIX compliant system" on your product
requirements box for doing this:

i = open ("blarg", O_WRONLY);
lseek(i, 0, SEEK_SET);
write(i, my_buffer, 2);
close(i);

This will not insert two bytes at the beginning. Rather it overwrites the
first two bytes.

 

[hdante]

What does "top-post" mean ?

I'm sorry, I thought that's what he wanted.

 

[Rolf Magnus]

What does "top-post" mean ?

It means that you are writing your text above the text you're answering to
instead of in a chronological order. I'll quote from Alf P. Steinbach's
signature:

A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

You should write your answers below the original text and directly below the
part that you are answering to. Also snip away parts that are not relevant
to your answer.

 

[Marcus Kwok]

What does "top-post" mean ?

http://en.wikipedia.org/wiki/Top_posting

Your responses should be interspersed thoughout the trimmed quoted text.