Hooking:
 
Server-boot, battle->check_target points to battle_check_target.
HPM stores the original address of battle->check_target.
Plugins initialise, hooking to battle->check_target causes the address of battle->check_target to change from battle_check_target to HP_battle_check_target, so calling battle->check_target gets to HP_battle_check_target.
 
HP_battle_check_target triggers the pre plugin (if any), runs the original address (battle_check_target), triggers post plugins (if any), and returns.
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int HP_battle_check_target( struct block_list *src, struct block_list *target,int flag) {
    int retVal;
    int i;
    
    /* hooks.battle_check_target_pre -> int */
    if( HPMHooks.count.HP_battle_check_target_pre ) {
        for(i = 0; i < HPMHooks.count.HP_battle_check_target_pre; i++ ) {
            retVal = (HPMHooks.list.HP_battle_check_target_pre[i])(src,target,&flag);
        }
    }
    
    retVal = HPMHooks.source.battle.check_target(src,target,flag);
    
    if( HPMHooks.count.HP_battle_check_target_post ) {
        for(i = 0; i < HPMHooks.count.HP_battle_check_target_post; i++ ) {
            retVal = (HPMHooks.list.HP_battle_check_target_post[i])(src,target,&flag,retVal);           
        }
    }
    
    return retVal;
}
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