How do I convert an integer to an enumerated type?

Question

I know how to convert an enumerated type to an integer.

type
  TMyType = (mtFirst, mtSecond, mtThird); 

var 
  ordValue:integer;
  enumValue:TMyType;
...
ordValue:= Ord(mtSecond); // result is 1

But how do I do the inverse operation and convert an integer to an enumerated type?

type TMyType = (mtFirst=1, mtSecond=2, mtThird=3); var ordValue:integer; enumValue:TMyType; ordValue:= Integer(mtSecond); // result is 2 — Engin Ardıç, Oct 20 '13 at 15:41

score 31 · Accepted Answer · edited Dec 14 '16 at 21:27

31

As Ken answered, you just cast it. But to make sure you have correct value you can use code like:

if (ordValue >= Ord(Low(TMyType))) and (ordValue <= Ord(High(TMyType))) then
    enunValue := TMyType(ordValue)
else 
    raise Exception.Create('ordValue out of TMyType range');

edited Dec 14 '16 at 21:27

Daniel Grillo

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answered Jan 04 '12 at 19:06

ain

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Oh you can use RTTI to get the allowable ranges and so tidy up this code – David Heffernan Jan 04 '12 at 19:17
1

@KenWhite AFAIK one can cast any (out of range) value to enum and it wont raise exception - you have to write the range check yourself. – ain Jan 04 '12 at 19:22
1

@ken what do you mean "automatically raise the exception"? – David Heffernan Jan 04 '12 at 19:26
No, AFAIK the high bits (which are out of enum range) are just disregarded and you get "random" enum value. No exception when then using it. – ain Jan 04 '12 at 19:33
@Ken I'm afraid ain has it right here. The only time that range checking code is emitted for enumerated types, that I am aware of, is when you perform arithmetic. And that means `inc` or `dec`. – David Heffernan Jan 04 '12 at 19:57
1

@David - less known now are `Succ` and `Pred` functions. – kludg Jan 04 '12 at 20:02
@Serg Ah yes, of course, and they get caught by range checking too – David Heffernan Jan 04 '12 at 20:07
@ain, `@David: I stand corrected. :) Deleting my comment as noise. – Ken White Jan 04 '12 at 20:09
Yes, this snippet requires severe cleanup. – OnTheFly Jan 04 '12 at 23:12
3

Beware when your enums are not contiguous. – Jeroen Wiert Pluimers Jan 05 '12 at 10:49

Ken White · Answer 2 · 2012-01-04T19:16:52.400

21

You can cast the integer by typecasting it to the enumerated type:

ordValue := Ord(mtSecond);
enumValue := TMyType(ordValue);

edited Jan 04 '12 at 19:16

answered Jan 04 '12 at 19:01

Ken White

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score 7 · Answer 3 · edited Dec 27 '13 at 20:00

7

Take care with casting because it requires full mapping with your ordinal type and integers. For example:

type Size = (Small = 2, Medium = 3, Huge = 10);
var sz: Size;
...
sz := Size(3); //means sz=Medium
sz := Size(7); //7 is in range but gives sz=outbound

edited Dec 27 '13 at 20:00

NGLN

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answered Dec 27 '13 at 18:26

user3140262

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How do I convert an integer to an enumerated type?

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