2.1 Ordinary constants

Ordinary constants declarations are not diﬀerent from the Turbo Pascal or Delphi implementation.

_________________________________________________________________________________________________________ Constant declaration
-- -- - - - ----------------------
constant declaration -identiﬁer--=---expression--;--|
___________________________________________________________________

The compiler must be able to evaluate the expression in a constant declaration at compile time. This means that most of the functions in the Run-Time library cannot be used in a constant declaration. Operators such as +, -, *, /, not, and, or, div, mod, ord, chr, sizeof, pi, int, trunc, round, frac, odd can be used, however. For more information on expressions, see chapter 8, page 254. Only constants of the following types can be declared: Ordinal types, Real types, Char, and String. The following are all valid constant declarations:

Const
  e = 2.7182818;  { Real type constant. }
  a = 2;          { Ordinal (Integer) type constant. }
  c = ’4’;        { Character type constant. }
  s = ’This is a constant string’; {String type constant.}
  s = chr(32)
  ls = SizeOf(Longint);

Assigning a value to an ordinary constant is not permitted. Thus, given the previous declaration, the following will result in a compiler error:

s := ’some other string’;

Prior to version 1.9, Free Pascal did not correctly support 64-bit constants. As of version 1.9, 64-bits constants can be speciﬁed.

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