How do I copy a file multiple times to make successively bigger files in C

Question

I need to make a number of large text files of varying sizes, in exact multiples of megabytes (in other words, exactly 10 MB, 50 MB, 100 MB, and I'm not sure how big I'll have to go).

I don't want the files to be all ones or zeroes, so I have a text file of about 10 MB, and I want to copy that text as many times as needed to make my files.

I have seen advice to use sendfile instead of read() and write(). I wrote something that will make a 1MB file from my 10MB file, but I wonder how I can loop around once I hit EOF to make a file of more than 10MB.

This will ultimately be used on a Linux computer but I'm writing it now in Cygwin (Windows) in C.

You can also use `dd` command with `if=/dev/urandom` or such to create a file that includes _not all ones or zeros_. — Etherealone, Nov 22 '13 at 22:17
Maybe it's just easier to make a random file of a certain number of megabytes that way, thanks. — punstress, Nov 22 '13 at 23:59

score 1 · Answer 1 · answered Nov 22 '13 at 22:17

1

If you're already navigating the file from start to finish and copying, all you're missing is a way to move back to the beginning.

When you hit EOF, use rewind():

rewind(file);

file is your file descriptor. rewind() is a special case of fseek():

fseek(file, 0, SEEK_SET); // Same effect

answered Nov 22 '13 at 22:17

salezica

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"Why use fseek() over rewind()?" - http://stackoverflow.com/questions/11839025/fseek-vs-rewind – Alex Reynolds Nov 22 '13 at 22:44
Wait a second, with sendfile I just do the call and it copies, I don't check for EOF ... – punstress Nov 22 '13 at 23:02
`fseek()` between `sendfile()` calls? – salezica Nov 22 '13 at 23:23

How do I copy a file multiple times to make successively bigger files in C

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