How to get the nid of current node

Question

I need a function to return the nid of the current node that the current user is watching. Can you help me?

Answer 1

If you are insisting on a function then you are looking for arg function.

arg(0) will return 'node' and arg(1) will return node nid.

Provided you must be inside a node.

[Updated Answer]

if (arg(0) == 'node' && is_numeric(arg(1))) {
  $nid = arg(1);
  if ($nid) {
    $node = node_load($nid);
    /** do something **/  
  }
}

Alternately

you can get nid from node object $node->nid

Answer 2

You can access $node object. $node->nid will return you NID of the node.

There is a hook to help you further to achieve something when user is viewing node - hook_node_view().

There are three parameter of the hook - $node (will return node object), $view_mode (view mode of the node like full or teaser) & $langcode (language code for rendering).

You can use this hook in your module & write your logic like -

function MYMODULE_node_view($node, $view_mode, $langcode){//replace your module name with MYMODULE here
  if($node->type == 'article' && $view_mode == 'full'){ //if content type is article & user is on full node view
    //do domething
  }
}