A statement which does not perform any action. A value of a guarded signal or an access variable.

Syntax:

[ label: ] null;  -- sequential_statement
null              -- value

Description:

The null statement is a sequential statement that does not perform any action and its only function is to pass on to the next statement. It is normally used within an if or case statement as an explicit way to take no action under certain conditions.

Null is also the value assigned to a guarded signal to mean disconnection, and the value assigned to an access variable by the procedure Deallocate(ptr).

The null statement is not mandatory, it is possible to leave a blank instead.

Example:

case Action is 
  when "001" => C := A and B; 
  when "010" => Q := null;      -- null value 
  when "100" => C := not A; 
  when others => null;          -- null statement 
end case;

See also:

Access, Case, If