[development] Set the CCK field value the the node is created

[David Hautbois]

Hi
I'm developping a custom CCK field for Drupal 6.
I'm don't want the user set the value himself. So, this field has no widget.

I'm looking for how to set the value when the node is saved. (the value 
is set when the node is created et not updated)
In hook_field, I tried to use 'presave' ou 'validate' for $op, but I've 
some problems to work with it :
- 'presave' seems to be called when the node is displayed...
- when the node is created, the field has no value ($items[0]['value'] 
does not exists)
- ...

I 've look in some others CCK fields, but no one work like this.

I copied the text_field CCK field, renamed all 'text_field' references, 
simplified it and removed the widget.

Can someone help me or point me to a good web page ? (not the CCK dev 
documentation !, I read it many times!)

Thanks.

David