Fragmenting and Un-fragmenting files in C - c

Question

I wanted to take a file (text or binary) and fragment it into small pieces of a certain size (about 250-500kB), randomize the order of the fragments, and put it into another temporary fragmented file.
The un-fragmenting would then take the fragmented file, extract the pieces, put them in order and allow the original file to be intact.
This would be very easy for simple text-based ASCII files as you could use the C library functions (like sscanf) for formating/parsing the information. The one file could have a format then like
(#### <fragment #> <fragment> ...)
However, I am not sure how one would do something like that with binary files.
I know one easy solution is to use separate files for the fragments like <.part1, .part2> files but this would be a bit ugly and wouldn't scale well to much larger files. It would be a lot better to just store it in one file.
Thanks a lot.

Answer 1

Doing this with binary files is easiest of all, and also the fastest and most reliable. Your fragment files need a simple segment record that gives you the offset in the original file and length of the segment. The record might look like this:
typedef struct _Fragment
{
unsigned long offset;
unsigned long length;
} Fragment;
Writing your file would go like this:
Fragment fragment;
FILE *outFile;
unsigned long segmentOffset, segmentLength;
char segmentData[MAXSEGMENTLENGTH];
outFile = fopen(fileName, "wb");
while (ReadNextSegment(segmentData, &segmentOffset, &segmentLength))
{
fragment.offset = segmentOffset;
fragment.length = segmentLength;
fwrite(header, sizeof(fragment), 1, outFile);
fwrite(segmentData, 1, segmentLength, outFile);
}
fclose(outFile);
Reassembling the file is accomplished by reversing the process. Read each Fragment record, then read the following data with fread using fragment.length, then position to the correct offset in the target file using the fseek function and fragment.offset, and then write it using fwrite.

Answer 2

Try to use binary data only. In you fragmented file, follow the structure:
OFFSET SIZE DESCRIPTION
0 4 BLOCK NUMBER
4 4 BLOCK SIZE IN BYTES
8 ? BLOCK DATA
Define a header structure:
typedef struct hdr
{
uint32_t number;
uint32_t size;
} hdr_t;
Code to work with it can look like:
void file_append(FILE *f, size_t block, size_t size, const void *data)
{
hdr_t hdr;
hdr.number = block;
hdr.size = size;
fwrite(&hdr, sizeof(hdr), 1, f);
fwrite(data, size, 1, f);
}
And reading the data:
void file_read_chunk(FILE *f, size_t *block, size_t *size, void **data)
{
hdr_t hdr;
fread(&hdr, sizeof(hdr), f);
*block = hdr.number;
*size = hdr.size;
*data = malloc(hdr.size);
fread(*data, hdr.size, 1, f);
}