[fpc-pascal]I don't understand value typecast
jonas at zeus.rug.ac.be
Tue Jul 2 16:11:50 CEST 2002
On zondag, juni 30, 2002, at 11:25 , Luis Del Aguila wrote:
> In the manual explain that the value typecast doesn't work, when the
> size of the expression and the size of the type cast not must be the
> (page 58. ref.pdf)
> But this program compile.
> Var a:integer;
> How work the value typecast?
I think the manual is incomplete. For ordinal-to-ordinal type casts
(integers/chars/booleans/range-types) and possibly also
ordinal-to-enumerations and vice versa, this same-size requirement
doesn't exist. In such a case,
a) when going from a smaller signed type to a larger signed type (e.g.
longint_var := longint(shortint_var)), the effect is the same as when
you would do a regular assignment (so if shortint_var contains $ff = -1
above, longintvar will become $ffffffff = -1)
b) when going from a smaller unsigned type to any larger type (e.g.
longint_var := longint(byte_var)), the value of the smaller type is
simply zero-extended (so if byte_var contains $ff = 255 above,
longint_var will become $ff = 255)
c) when going from a larger to a smaller type, you just take the n lower
bytes of the larger type and copy them into the smaller type, where n =
the size in bytes of the smaller type.
Char, Boolean and all enumeration types (which don't have an explicit
lower bound set that's negative) are treated as unsigned.
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