during copy transform constraint, the child object snaps to the origin point of the parent object When i use the copy transformation constraint, the child object snaps to the origin point of the parent object. 

What i want is, when i constraint an object, the child object should remain where it is, but when i move the parent object, the child should move with it, maintaining the distance and the rotation offset between them.
It looks like the Copy Transforms doesn't have any Offset option (I don't know why), so I guess if you want it to copy each of its target's transformation you need instead to give it a Copy Location constraint (enable the Offset option), a Copy Rotation and a Copy Scale.