Section: Inspection Functions
y = isfield(x,field)
and returns a logical 1 if x has a field with the 
name field and a logical 0 if not.  It also returns
a logical 0 if the argument x is not a structure array.
--> a.foo = 32
a = 
    foo: 32
--> a.goo = 64
a = 
    foo: 32
    goo: 64
--> isfield(a,'goo')
ans = 
 1 
--> isfield(a,'got')
ans = 
 0 
--> isfield(pi,'round')
ans = 
 0