Thread: The best way to delete a record from a file?

Hi ALL,

Lets say I have a file name "cars.bin".
Each record in the file is a struct (made from int, char [20], int).
Lets say I have 10000 records,
struct 1, struct 2, struct 3, struct ....., struct 10000.

Now, If I want to delete record #400, how should I do it??
The only thing I could think of is to:
1. Create a new file
2. Copy all the records from old file to new file (except of the #400)
3. Delete old file
4. Rename new file to old file name.

This seem like a slow poor solution, is there any other way to do it?

Many thanks
Salvador

Since all the structures are the same size, you could open the file, seek to structure 10,000, copy it to structure #400 position, then resize the file to be smaller by one structure.

This would be very fast.

Todd

This dilemma is why databases were invented.

Cheers!

How do I resize a file?

Since all the structures are the same size, you could open the file, seek to structure 10,000, copy it to structure #400 position, then resize the file to be smaller by one structure.

This would be very fast.

Todd

I don't get exactly how this would work. Would you not need to move the structure instead of copy it?

Say each entry is a line of text, then to actually delete it you would have to copy all the following text over it, then resize the file. Or am I missing something here?

Personally I like matsp's suggestion, which sounds easy to do.

On unix, you would use truncate().

Originally Posted by mike_g

I don't get exactly how this would work. Would you not need to move the structure instead of copy it?

Say each entry is a line of text, then to actually delete it you would have to copy all the following text over it, then resize the file. Or am I missing something here?

Personally I like matsp's suggestion, which sounds easy to do.

move==copy. Same thing.

Oh yeah, actually I get it now (i think). You could just swap the entry to be deleted with the last entry then truncate it. So yeah both ways would be fast

I will adapt mat's suggestion too if the file is sorted. (thank you)
and Todd's if not (thank you too)
I still don't understand how can I resize a file size on Windows....

On Windows, _chsize().