Program to open a file in binary, skip X bytes and write the rest of the file to a new file

[scad]

How would I approach this? I cannot store the entire file in memory
(they are 30GB+) but I need to skip the first 292 bytes and write the
rest to a new file.

Thanks,

Scott

[Victor Bazarov]

1. Open the file to read (file_1)
1.a If file_1 in bad state, report and exit.

2. Counter = number of bytes to skip
3. While counter > 0 and not the end of file_1
read file_1

3.a. If file_1 in bad state, report and exit.

4. Open the file to write (file_2)
4.a If file_2 in bad state, report and exit.

5. While not the end of file_1
read file_1 into 'buffer'
if successful, write 'buffer' to file_2
if file_2 in bad state, report and exit.

V
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I do not respond to top-posted replies, please don't ask

[mzdude]

On May 27, 2:03 pm, Victor Bazarov <v.Abaza...@comAcast.net> wrote:
> scad wrote:
> > How would I approach this?  I cannot store the entire file in memory
> > (they are 30GB+) but I need to skip the first 292 bytes and write the
> > rest to a new file.
>
>     1. Open the file to read (file_1)
>     1.a   If file_1 in bad state, report and exit.
>
>     2. Counter = number of bytes to skip
>     3. While counter > 0 and not the end of file_1
>          read file_1

optional step
2. Look up the function seek()

>
>     3.a.  If file_1 in bad state, report and exit.
>
>     4. Open the file to write (file_2)
>     4.a   If file_2 in bad state, report and exit.
>
>     5. While not the end of file_1
>          read file_1 into 'buffer'
>          if successful, write 'buffer' to file_2
>          if file_2 in bad state, report and exit.

If I know I'm dealing with large files, I might even check available
disk space before starting the copy. Hate to get 29G into the copy
and fail due to lack of disk space.

[Victor Bazarov]

I don't think C++ has the means to do that.

[James Kanze]

On May 27, 9:03 pm, Victor Bazarov <v.Abaza...@comAcast.net> wrote:
> scad wrote:
> > How would I approach this? I cannot store the entire file
> > in memory (they are 30GB+) but I need to skip the first 292
> > bytes and write the rest to a new file.

> 1. Open the file to read (file_1)
> 1.a If file_1 in bad state, report and exit.

> 2. Counter = number of bytes to skip
> 3. While counter > 0 and not the end of file_1
> read file_1

You could also just use istream::ignore. (Otherwise, of course,
you'll also want to decrement counter by the number of bytes
you've read each time:-).)

> 3.a. If file_1 in bad state, report and exit.

> 4. Open the file to write (file_2)
> 4.a If file_2 in bad state, report and exit.

> 5. While not the end of file_1
> read file_1 into 'buffer'
> if successful, write 'buffer' to file_2
> if file_2 in bad state, report and exit.

If there's an error in writing the file, I generally like to
delete it before exiting, so that the corrupt version doesn't
accidentally get used.

--
James Kanze (GABI Software) email:james...@gmail.com
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