Use scoped_ptr when

• A pointer is used in a scope where an exception may be thrown

• There are several control paths in a function

• The lifetime of a dynamically allocated object can be limited to a specific scope

• Exception safety is important (always!)

Use shared_ptr in the following scenarios:

      When there are multiple clients of an object, but no explicit owner

• When storing pointers in Standard Library containers

• When passing objects to and from libraries without (other) expressed ownership

• When managing resources that need special cleanup^[9]

Use weak_ptr to

• Break cyclic dependencies

• Use a shared resource without sharing ownership

• Avoid dangling pointers

check:http://my.oschina.net/jackwgm/blog/6695?catalog=23886