Section 465 of the CrPC embodies the principle that a finding or sentence should not be reversed or altered on account of any error, omission, or irregularity unless it has occasioned a "failure of justice." This section is for curing procedural irregularities that are not fundamental.
(a), (b), and (c) are serious irregularities that go to the root of a fair trial and jurisdiction, and are generally considered incurable as they cause prejudice and a failure of justice.
(d) Non-compliance with Section 235(2) refers to the failure of a judge to hear the accused on the question of sentence after conviction. The Supreme Court has held that this is a curable irregularity. Instead of setting aside the conviction, the appellate court can remand the case back to the trial court for the limited purpose of hearing the accused on the sentence.