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BoolToStr causes Undeclared Identifier error

Posted on 2007-11-16
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Last Modified: 2010-04-21
I need to convert a boolean value to a string, but BoolToStr does not work. Why?

I'm using Delphi 5.0

Thanks,

J
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Question by:JonathanGSK
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12 Comments
 
LVL 19

Expert Comment

by:MerijnB
ID: 20300259
that is strange, BoolToStr is not really something difficult,

can you show some code?
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Accepted Solution

by:
Johnjces earned 100 total points
ID: 20300489
I refreshed! :)

Delphi 5 does not have BoolToStr.

Here is a code snippet from Koders Code Search...

function BoolToStr(B: Boolean; UseBoolStrs: Boolean = False): string;
const
  cSimpleBoolStrs: array [boolean] of String = ('0', '-1');
begin
  if UseBoolStrs then
  begin
    VerifyBoolStrArray;
    if B then
      Result := TrueBoolStrs[0]
    else
      Result := FalseBoolStrs[0];
  end
  else
    Result := cSimpleBoolStrs[B];
end;

Their URL is:

http://www.koders.com/delphi/fid53147BF1A84109076F2982F8935A5A188DE37B0C.aspx

John
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LVL 19

Expert Comment

by:MerijnB
ID: 20300517
and I didn't read the question thoroughly enough...

Johnjces posst looks good, I just wonder if TrueBoolStrs and FalseBoolStrs are available in D5?
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Expert Comment

by:Johnjces
ID: 20300601
MerijnB

I could not find it anywhere in my D5 install.

All of that is declared/defined in the  PXDelphi5.pas posted by Koders Code Search... same URL as above.

John
0
 
LVL 25

Expert Comment

by:imitchie
ID: 20303994
is it not easier to write your own?
function BoolToStr(B: Boolean): string;
const
  cTrueFalseString: array [boolean] of String = ('true', 'false'); // change this
begin
  Result := cSimpleBoolStrs[B];
end;

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LVL 11

Expert Comment

by:ZhaawZ
ID: 20304174
imitchie, I think it should be  "(false, true)" :)

And I'd advise to use "if b then result := cTrueFalseString[true] else result := cTrueFalseString[false]", otherwise there could be situations when your function won't work:

var
    b : boolean;
begin
b := boolean(2);
ShowMessage(BoolToStr(b)); // your function; crashes
ShowMessage(SysUtils.BoolToStr(b, true)); // default D6's function; shows "true"
end;

"2" in "b := boolean(2)" could be result of some function which is not written by you, so such situations are possible.
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LVL 45

Expert Comment

by:aikimark
ID: 20306368
somethings missing or altered from Koders snippet:

{ StrToBool converts the given string to a boolean value.  If the string
  doesn't contain a valid value, an EConvertError exception is raised.
  BoolToStr converts boolean to a string value that in turn can be converted
  back into a boolean.  BoolToStr will always pick the first element of
  the TrueStrs/FalseStrs arrays. }

var
  TrueBoolStrs: array of String;
  FalseBoolStrs: array of String;

const
  DefaultTrueBoolStr = 'True';   // DO NOT LOCALIZE
  DefaultFalseBoolStr = 'False'; // DO NOT LOCALIZE

function BoolToStr(B: Boolean; UseBoolStrs: Boolean = False): string;

procedure VerifyBoolStrArray;
begin
  if Length(TrueBoolStrs) = 0 then
  begin
    SetLength(TrueBoolStrs, 1);
    TrueBoolStrs[0] := DefaultTrueBoolStr;
  end;
  if Length(FalseBoolStrs) = 0 then
  begin
    SetLength(FalseBoolStrs, 1);
    FalseBoolStrs[0] := DefaultFalseBoolStr;
  end;
end;

function BoolToStr(B: Boolean; UseBoolStrs: Boolean = False): string;
const
  cSimpleBoolStrs: array [boolean] of String = ('0', '-1');
begin
  if UseBoolStrs then
  begin
    VerifyBoolStrArray;
    if B then
      Result := TrueBoolStrs[0]
    else
      Result := FalseBoolStrs[0];
  end
  else
    Result := cSimpleBoolStrs[B];
end;
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LVL 25

Expert Comment

by:imitchie
ID: 20306498
zhaawz, i learned something new today!  I have refined the function

i never knew
var b: boolean
b := Boolean(2) is valid!
function BoolToStr(B: Boolean): string;
const
  cTrueFalseString: array [boolean] of String = ('false', 'true'); // change this
begin
  if B then
    Result := cTrueFalseString[false]
  else
    Result := cTrueFalseString[true];
end;

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0
 
LVL 25

Expert Comment

by:imitchie
ID: 20306502
except.. it is true =0, false=1
cos i debugged it
function BoolToStr(B: Boolean): string;
const
  cTrueFalseString: array [boolean] of String = ('true', 'false'); // change this
begin
  if B then
    Result := cTrueFalseString[false]
  else
    Result := cTrueFalseString[true];
end;

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0
 
LVL 11

Expert Comment

by:ZhaawZ
ID: 20306766
"except.. it is true =0, false=1"

if 0, then false, otherwise true ;) it has been like that for many years.


>> begin
>>   if B then
>>     Result := cTrueFalseString[false]
>>   else
>>     Result := cTrueFalseString[true];
>> end;

why do you return false on "if b"? "if b" is the same as "if b = true", so if it's true, you're returning "false" string, but if it's false, you're returning "true" string.
0
 
LVL 45

Expert Comment

by:aikimark
ID: 20308045
In Delphi, False and True are an enumeration of a boolean set.  As such, they have implied numeric values that are indexes into their positions in the [False, True] set.
0
 

Author Closing Comment

by:JonathanGSK
ID: 31409596
Thanks to everyone who contributed to a VERY thorough analysis of this problem. John's answer is correct - I guess it's time to upgrade to Delphi7!

I have been using a very inelegant line, which works:

if Flag=True then String1:='True' else String1:='False';

But thanks for the alternatives,

Jonathan
0

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