struct - Structure declaration in c with identifer -

i try understand c code:

typedef struct _intelem *intlist; typedef struct _intelem { int head; intlist tail;} intelem; 

i understand defines recursive type, list. don't understand way declared. understand second line, define structure named intelem consists of integer , intlist. _intelem in declaration?

the first line allocates memory list?

• the first line

   typedef struct _intelem *intlist; 

is create typedef or alias struct _intelem *. alias named intlist. fwiw, @ point of time, definition of struct _intelem need not known compiler.

• the second line

  typedef struct _intelem { int head; intlist tail;} intelem; 

  1. actually defines user-defined type _intelem, 2 members, head int , tail intlist(typedefed earlier)
  2. typedef type intelem.

please note: there no variable created, either of type (s) (i'm not talking member variables, of course, part of definition). so, there no memory allocated , such.

so, explicit

but _intelem in declaration?

the _intelem name of user-defined data type. however, in cases, optional. example,

typedef struct { char name [32]; int age; float salary;} employee; 

is both fine , legal, except fact, in case, we're creating alias employee unnamed data type.