sql Loader read file with more or less column

I need to create a .ctl file that can read source file wit less or more row... Example

file a: a;b;c

file b: a;b

load data
APPEND 
into table table_of_parameter
fields terminated by ";" optionally enclosed by '"'
TRAILING NULLCOLS
(
parameters1,
parameters2,
parameters3
)

and I want this:

select * from table_of_parameter

parameters1 parameters2 parameters3

 a              b              c
 a              b           null (o something else)

there's a way to do this on ctl file?