how can fstream not overwite filedata?

[larryG]

does anybody know how can i insert data to a file in between the previous data??
eg if a file content is :
"123456789"
and i want to insert "abc" between 4 and 5 so that the file content will be
"1234abc56789"
without having to read the rest of the file,save it somewhere else and then re-insert it

i am trying to construct a b+ tree and this is really important

thank you in advance

[Duthomhas]

Think of a file as an array of char.
For example

char mydata[ 50 ] = { 1, 3, 5, 9, 11, 13 };

How do you put a 7 in there between 9 and 11?

Unless your file is particularly huge, it is often easier just to load the whole thing into memory, make your changes, then write it back out.

I hope this gives you some ideas.

[helios]

Another way is to use a temporary file.
You want to insert y bytes at offset x:
Copy bytes 0 to x-1 from file f to a new file f2. Write the y bytes to file f2. Copy bytes x to n-1 from file f to f2. Delete f. Rename f2 to f.

[larryG]

thanx but loading it to memory or working with 2 file streams is something i want to avoid.Any other ideas are welcome :)

[jsmith]

Insertion of data into the middle of a file is not a typical operation supported by a filesystem. Said another way, I think you are out
of luck. You'll probably need to do as helios said.

[Duthomhas]

You can do it without the temporary file. Remember, think of your file as if it were an array. As a hint, treat each element of the array as a 'string' of length <number of bytes to insert>. You'll need a couple of look-ahead buffers and random access on the file.

Hope this helps.