Asolenoidis a cylindrical coil of wire whose diameter is small compared to its length.

The poles of the bar magnet do not lie exactly on the end of the magnet but is somewhat inside. In solenoid poles can be considered to be lying at the edge.

2) The magnetism retains in the bar magnet naturally but in solenoid the magnetism is there so long current flows through it.

3) Magnetic field of a bar magnet emanates from throughout the body of the magnet, with more intensity at the poles. While there is no field emanating from the lateral surface of the solenoid.The nature of magnetic field lines produced by a solenoid is similar to that of a bar magnet.the field lines are closed curves, they emerge from the north pole and merge in the south pole outside the magnet and inside the direction is from south to north.inside the solenoid and a bar magnet the field is uniform.the poles in a solenoid can be determined by using a bar magnet or by clock face rule.