help with fwrite()

[T. Crane]

Hi all,

I'm trying to use successive calls to fwrite() to write out to a file.
I don't have any trouble opening the file or getting everything I need
in there, but I do notice a peculiarity about it that I will describe.

I call it like so:

fwrite(&buffer, 14, 1, filestream)

I then call it may times in a loop where I've set my buffer pointer to
change with each iteration so that it writes the data I want it to
write. When I go into debug mode, I can then open up the file in a
reader and watch it grow, so to speak. The odd thing is that it
doesn't seem to grow with every call to fwrite(). It only seems to
grow in 4 kB jumps. Does anyone know why this would be?

FYI - I'm using Windows XP and my compiler is Visual C++ 6.0.

thanks in advance,
trevis

 

[Alf P. Steinbach]

* T. Crane:

Hi all,

I'm trying to use successive calls to fwrite() to write out to a file.
I don't have any trouble opening the file or getting everything I need
in there, but I do notice a peculiarity about it that I will describe.

I call it like so:

fwrite(&buffer, 14, 1, filestream)

I then call it may times in a loop where I've set my buffer pointer to
change with each iteration so that it writes the data I want it to
write. When I go into debug mode, I can then open up the file in a
reader and watch it grow, so to speak. The odd thing is that it
doesn't seem to grow with every call to fwrite(). It only seems to
grow in 4 kB jumps. Does anyone know why this would be?

Buffering.


Cheers, & hth.,

- Alf

 

[Pete Becker]

I'm trying to use successive calls to fwrite() to write out to a file.
I don't have any trouble opening the file or getting everything I need
in there, but I do notice a peculiarity about it that I will describe.

I call it like so:

fwrite(&buffer, 14, 1, filestream)

I then call it may times in a loop where I've set my buffer pointer to
change with each iteration so that it writes the data I want it to
write. When I go into debug mode, I can then open up the file in a
reader and watch it grow, so to speak. The odd thing is that it
doesn't seem to grow with every call to fwrite(). It only seems to
grow in 4 kB jumps. Does anyone know why this would be?

Output streams are usually buffered by the runtime library, and 4k is
certainly a reasonable size for that buffer. The contents of the buffer
only get written to disk when the buffer gets full or you close the
file.

 

[T. Crane]

OK that's pretty much what I guessed, but I thought I'd ask.

thanks for the confirmation.

 

[Jalen]

OK that's pretty much what I guessed, but I thought I'd ask.

thanks for the confirmation.

One thing i want to know is whether there is a way to change the
buffer size (currently 4K)?

Thanks
Jalen

 

[Pete Becker]

One thing i want to know is whether there is a way to change the
buffer size (currently 4K)?

Yes, there is. Look it up.