How to save trees on files?

[hanaa]

Hello
I am trying to use tree data structures in an address book. Would someone tell me how the nodes..that is.. a tree can be saved in a file.? A file, Or any other method through which the tree can saved onto the computer.
I had made the address book in C just using structures. And saved them onto files using fread, fwrite etc. I want to make modifications in it, to now use C++, and trees for it to be more efficient
Thank you
Hanaa

[weaknessforcats]

Just write the key and the value to the disc. You should have a sequential file of these key/value pairs.

To restore the tree, you create an empty one, read a key/value from the disc an insert it in the new tree.

Then just do the same for the other key/value pairs.

There is no need to preserve the actual tree structure in the disc file.

[hanaa]

I'm afraid I didnt completely understand. I tried to do it. I couldnt. Would you please show me a simple illustrative piece of code..(esp, on how to read the sequential file contents into the tree..).
thank you,
Hanaa

[weaknessforcats]

Pseudo-code:
To store tree:
1) Create emtpy disc file or posittion to beginning if existing
2) Read Tree to get key/value
3) Write key/value to disc file
4) Repeat 2 and 3 until all keys in the Treee have been read.


To load from disc:
1) Create empty tree.
2) Read key/value from disc
3) Insert in tree
4) Repeat 2 and 3 until disc file EOF is reached.

[Orensh]

For an arbitrary tree (where there are no rules in the construction of the tree) you may need to store info about the parent of each node.
something like:
<id>, <parent>, <data>

for example:
<1>, <0 -- this means this is the root>, <"I am the root">
<2>, <1>, <"I am the first child">
<3>, <1>, <"I am the second child">
<4>, <2>, <"I am the grandchild">

hope this helps,
Oren

[weaknessforcats]

[quoteOrensch]
<1>, <0 -- this means this is the root>, <"I am the root">
<2>, <1>, <"I am the first child">
<3>, <1>, <"I am the second child">
<4>, <2>, <"I am the grandchild">
[/quote]

Generally you shouold not need to do this unless you desire to have the disc file be the actual tree. In which case the <1>, <4>, etc.. would be seek offsets from the beginning of the file.

I have seen flat disc files containing the key/value pairs that are processed by a utility to do just as you suggest with the result in a second file called the index file. Then you use the index file to get to offset of the record in the data file.

I just don't know if that is the case here.