Evening,

"Tan, Qiye via Libstdc++" <libstdc++@gcc.gnu.org> writes:

> I'm new in C++ who have an interest in the implementation of C++ STL.
> Recently, I tried to implement my own vector template. However, when I
> implemented my own iterator, I found that I had no idea how to
> detect whether it is dereferencable. Therefore, I began to explore the
> libstdc++, but I found that for some member functions, I can only find the
> declaration but no definition. For example, the 'bool
> __gnu_debug::_Safe_iterator_base::_M_singular(  ) const', 'void
> __gnu_debug::_Safe_iterator_base::_M_detach(  )', etc. They are declared in
> 'libstdc++-v3/include/debug/safe_base.h'. I can guess that '_M_singular'
> may just check if '_M_sequence' is NULL, but I still want to find their
> definition. Can someone help me? Thank you so much.

_M_singular() and _M_detach() are implemented in src/c++11/debug.cc.  A
complete iterator implementation technically doesn't need either, these
are used for debugging purposes in libstdc++, see also
https://gcc.gnu.org/onlinedocs/gcc-12.2.0/libstdc++/api/a05206.html

Do keep in mind that the __gnu_debug namespace is only used in case that
_GLIBCXX_DEBUG is set, see
https://gcc.gnu.org/onlinedocs/gcc-12.2.0/libstdc++/manual/manual/debug_mode.html

Hope that helps, have a great night!
-- 
Arsen Arsenović