Program to open a file in binary, skip X bytes and write the rest ofthe 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]

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

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

 

[mzdude]

    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]

optional step
2. Look up the function seek()

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.

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

V

 

[James Kanze]

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.