At line 109 of share_ptr (version 1.30.2) is the init list shared_ptr(): px(0), pn() which uses the default constructor for pn, which has type shared_count. However, there appears to be no such default constructor in shared_count. Am I missing something? Andrew P.S.: Forgive me if the answer appears somewhere easily searchable. I was unable to find an archive for bug reports or for this list. Pointers to such resources will be welcome.