[myvahid]

You can use trailingslash*t() for making safe URL

Group permalink example :

$group = groups_get_group( array( ‘group_id’ => $group_id ) );
$group_permalink = trailingslash*t( bp_get_root_domain() . ‘/’ . bp_get_groups_root_slug() . ‘/’ . $group->slug . ‘/’ ) );

trailingslash*t => * = i

[myvahid]

This should work

$group = groups_get_group( array( 'group_id' => $group_id ) );
$group_permalink = trailingslash*t( bp_get_root_domain() . '/' . bp_get_groups_root_slug() . '/' . $group->slug . '/' ) );

replace *=i