6

Pascal Set Types

In Pascal, a set type is implemented as a bit vector, which is similar to a C short-word array, where each short-word contains two bytes. Thus, sets are bit-vectors, and they are allocated in multiples of 16 bits. To find out the size of a set, enter the following code:

ceiling( ord( highest_element ) / 16 )

Direct access to individual elements of a set is highly machine-dependent and should be avoided.

General Parameter Passing in C and Pascal

A few general rules apply to parameter passing:

•C passes all arrays by reference since C strings are arrays.

•C passes all structures by value.

•In C, if you want to pass anything else by reference, then you must explicitly prepend the reference ampersand (&), or pass an explicit pointer.

•Pascal passes all parameters by value unless you explicitly state that they are var, in out, or out parameters, in which case they are passed by reference.

Procedure Calls: C–Pascal

Here are examples of how a C main program calls a Pascal procedure:

The Pascal procedure, Samp, in the file Samp.p. Note the procedure definition.

procedure Samp(var i: integer; var r: real); begin

i := 9; r := 9.9

end; { Samp }

The C–Pascal Interface

93