ISFILE() Function and %TRUE

[Jean-Pierre LEROY]

Hello,

I found the new function ISFILE() very useful.

At first I used it the wrong way like that :

IF ISFILE(lFilename) = %TRUE THEN ...

This code could not work properly; I understood later that I was wrong because from the documentation, the value true (-1) is returned when the file is found and the value for the numeric equates %TRUE is 1; so here is my question :

Why the true value (-1) returned by the ISFILE function is different from the numeric equates %TRUE (1) defined in Win32API.inc ? or why the value for numeric equates %TRUE is 1 and not -1 in Win32API.inc ?

Thanks
Jean-Pierre

[Michael Mattias]

%TRUE in Windows-speak is "non-zero" and may be defined as any non-zero value; that is your code - if properly written - should work if you define:

%TRUE = 8752019

The PB "ISTRUE" function could be defined with a MACRO:

MACRO ISTRUE (X) =  IIF& (X <> 0, -1&, 0)

You ISFILE code would have worked had you coded..

  IF ISTRUE ISFILE(fileSpec) THEN 
  ...

or even

 IF ISFILE (filespec) THEN

.. either of which would be a better way to code it.

You think this is confusing, throw in a few NOTs and then tell us with a straight face you don't appreciate ISTRUE's sibling, ISFALSE.

[Cliff Nichols]

Or short and sweet
%False = 0
%True = (well it depends on the function asked, but truthfully would be ANYYYYYTHING that is not zero) and it is up to the question that is asked if so called "TRUE" or "False"

[Mel Bishop]

This works for me:
%false = 0
%true = not %false

By MM
...throw in a few NOTs ...

[Jean-Pierre LEROY]

Michael, Cliff and Mel,

Thank you for your answers.

I appreciate your support.

[Hubert Brandel]

to clearly understand, have a look in the Helpfile "ISFALSE and ISTRUE operators" ... or see this

? Isfile() -> 0 or -1
? NOT Isfile() -> -1 or 0

inside (Power)Basic it is no Problem to ask with 'NOT',
but with the Windows API ...

? %true -> 1 'OK
? not %true -> -2 (this should be 0 )
? %false -> 0 'OK
? not %false -> -1 'OK

[Kev Peel]

It's pretty simple, all you need to do is to check whether the value is FALSE or not, if it's not FALSE then it's TRUE (any arbituary value).

 IF (val <> %FALSE) THEN
   ' Value is TRUE
END IF
 
IF (val = %FALSE) THEN
   ' Value is FALSE
END IF

FALSE is ALWAYS zero with PowerBASIC and the Win32 API. No exceptions.

[Michael Mattias]

As far as I am concerned, you should NEVER test a variable for equality with TRUE or FALSE; you should always use ISTRUE and ISFALSE.

Maybe with FALSE it's OK, but certainly not with TRUE.

MCM

[colin glenn]

My previous workaround for something like this used to be:

IF NOT (variable = 0) THEN ...

[Michael Mattias]

FALSE is ALWAYS zero with PowerBASIC and the Win32 API. No exceptions

TRUE and FALSE are logical concepts, not integer values.

However, since few BASICs support a LOGICAL or BOOLEAN data type, as far as I can recall TRUE and FALSE have always been implemented as either an on/off BIT or a non-zero/zero integer.

MCM

[Patrice Terrier]

Just use the boolean function value like this:

IF ISFILE(lFilename) THEN

OR

IF NOT ISFILE(lFilename) THEN

then no need to make further comparison...

[Kev Peel]

TRUE and FALSE are logical concepts, not integer values.

Not in PB/WIN they aren't. In PB, values are compared, not concepts.

I've made my point, no further discussion required.