wp-includes/user.php:654Gets the current user's ID.
intfunction get_current_user_id() { if ( ! function_exists( 'wp_get_current_user' ) ) { return 0; } $user = wp_get_current_user(); return ( isset( $user->ID ) ? (int) $user->ID : 0 );}Introduced in MU (3.0.0). Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/user.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.