Magnetic Field Inside Cylindrical Conductor

[pardesi]

why is the magnetic field just inside a cylindrical conductor with inner radii a, and outer radii b carrying a uniform current I distributed through it's croos section just 0 inside the conductor.
I used ampere's law and that surely doesn't give 0

 

[granpa]

a current produces a magnetic field whose lines of force form circles around the wire carring the current. every loop (of field lines) must inclose a current and there is no current in the hollow part of the wire.