Question

How do i get the user id from user login name in wordpress?

Answer 1

By using get_userdatabylogin:

$user = get_userdatabylogin('loginname');
if($user){
   echo $user->ID;
}

Example:

$user = get_userdatabylogin('admin');
if($user) echo $user->ID; // Outputs 1

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UPDATE: the function get_userdatabylogin has been deprecated, and replaced with get_user_by(). Refer to Dalen’s solution to this question.