ios - Pop to root view in an unwind segue -

my view controller sequence follows:

a -> (push) -> b -> (modal) -> c

i return c b using unwind segue , works.

i return directly c a.

in unwind segue located in b, try pop root view:

-(ibaction)unwindtobfromc:(uistoryboardsegue *)segue {     [self.navigationcontroller poptorootviewcontrolleranimated:yes]; } 

and error:

tried pop view controller doesn't exist. 

when execute:

[self.navigationcontroller poptorootviewcontrolleranimated:yes]; 

in b in button action return no problem. what's wrong?

since c in modal, there nothing pop to. dismiss instead.

[self dismissviewcontrolleranimated:yes completion:nil];