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Null Statement

Formal Definition

A statement which does not perform any action.

Simplified Syntax



The null statement does not perform any action and its only function is to pass on to the next statement. It can be used to indicate that when some conditions are met no action is to be performed. Such an application is useful in particular in conjunction with case statements to exclude some conditions (see example).


case OPCODE is
  when "001" => TmpData := RegA and RegB;
  when "010" => TmpData := RegA or RegB;
  when "100" => TmpData := not RegA;
  when others => null;
end case;

The example shows an operand detection of a processor, restricted to some simple logical operations performed on registers. All other operations are blocked ("if the OPCODE is other than the explicitly listed, do nothing").

Important Notes

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