View source for r7.1.1:Macro LFDS711 BTREE AU SET KEY IN ELEMENT

{{DISPLAYTITLE:macro LFDS711_BTREE_AU_SET_KEY_IN_ELEMENT}}
==Source File==
 └───liblfds711
     └───inc
         └───liblfds711
                 lfds711_btree_addonly_unbalanced.h

==Opaque Structures==
 struct [[r7.1.1:struct lfds711_btree_au_element|lfds711_btree_au_element]];

==Macro==
 #define LFDS711_BTREE_AU_SET_KEY_IN_ELEMENT( btree_au_element, new_key )

==Parameters==
''btree_au_element''
: A ''struct lfds711_btree_au_element'', which is not currently part of a tree.  Not a pointer to it - the struct itself.

''new_key''
: A pointer, which will be cast by the macro to a ''void *'', which the key in ''btree_au_element'' is set to.

==Return Value==
No return value.

==Notes==
The key can only be set before an element enters the btree.  If it is set after, the btree will likely be broken (as the new key, being different to the old key, would most likely require the element to be in a different position in the tree, and this element movement is not supported) and also, key is not set atomically, so that even if a change was made, there is in principle no guarantee any other logical core would see that change anyway.

Key is not set atomically because it is known it will only be set before an element enters the tree.  Matters can be (and have been) arranged to ensure key is despite the lack of an atomic set correctly propagated to other logical cores, but this is a behaviour of the linking code, not of the macro which sets key.

As with all ''liblfds'' macros, the macro operates on the structure itself, not a pointer to it.

==Example==
 #include <stdio.h>
 #include "liblfds711.h"
 
 struct test_data
 {
   int long long unsigned
     unique_id;
 
   char
     payload[64];
 
   struct lfds711_btree_au_element
     buae;
 };
 
 int key_compare_function( void const *new_key, void const *existing_key )
 {
   int
     cr = 0;
 
   int long long unsigned
     *new_key = (int long long unsigned *) new_key,
     *existing_key  = (int long long unsigned *) existing_key;
 
   if( *new_key > *existing_key )
     cr = 1;
 
   if( *new_key < *existing_key )
     cr = -1;
 
   return( cr );
 }
 
 int main()
 {
   struct lfds711_btree_au_element
     *buae;
 
   struct lfds711_btree_au_state
     baus;
 
   struct lfds711_misc_prng_state
     ps;
 
   struct test_data
     td = { 15, "Tellurium-128" },
     *temp_td;
 
   lfds711_misc_library_init_valid_on_current_logical_core();
 
   lfds711_misc_prng_init( &ps );
 
   lfds711_btree_au_init_valid_on_current_logical_core( &baus, key_compare_function, LFDS711_BTREE_AU_EXISTING_KEY_FAIL, NULL );
 
   LFDS711_BTREE_AU_SET_KEY_IN_ELEMENT( td.baue, &td.unique_id );
   LFDS711_BTREE_AU_SET_VALUE_IN_ELEMENT( td.baue, &td );
   lfds711_btree_au_link( baus, &td.baue, NULL, &ps );
 
   lfds711_btree_au_get_by_position( &baus, &baue, LFDS711_BTREE_AU_ROOT );
 
   temp_td = LFDS711_BTREE_AU_GET_VALUE_FROM_ELEMENT( *baue );
 
   printf( "payload in element is \"%s\"\n", temp_td->payload );
 
   lfds711_btree_au_cleanup( &baus );
 
   lfds711_misc_library_cleanup();
 
   return( EXIT_SUCCESS );
 }

==See Also==
* [[r7.1.1:Binary Tree (add-only, unbalanced)|Binary Tree (add-only, unbalanced)]]