How to save tree?
lazarus / 3-General

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kernel · 2009-11-26 15:17

Hi
I thought it would be like code below, but it doesn't work. What's
wrong? Thanks for help.

var
  Tree1 : Tree
  f : File of Tree;
begin
  assignFile(f, 'file.dat');
  rewrite(f);
  Seek(f,0);
  write(f, Tree1);
  closeFile(f);
end;

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theo · 2009-11-26 16:58

Whrere / how is "Tree" defined?

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Blaazen · 2009-11-26 17:11

Hi,
I don't know what is exactly your type Tree, but probably it is some
tree structure with your data (like AVL tree). It means if you try to
save Tree to file this way you only save some pointers which are used
for realization of Tree and some pointers to your data, but not data
itself.
I think solution is go step by step through Tree and save all data to
file (probably it is records).
When file is opened next time, you create new empty Tree and you add
new elements and make them points to your data step by step until you
reach end of file.
I think it is similar to all dynamic structures, it is simplier for
lists (one or bi-directional) and more difficult for Trees (because
they are usually sorted).

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Troodon · 2009-11-26 18:29

If Tree is a pointer to a record then try write(f, Tree1^). But if
Tree is a data structure that contains pointers then, like Blaazen
said, in order to save the data to a file you need to traverse the
structure.