On 08/28/14 07:18, Tim Lewis wrote:
> It appears that this should prevent the display of the text statement.
> However, to my surprise, it works on NT32. Per operator precedence, it
> should be 8|8 is 8, and 8 == 8 is TRUE.
>
>
>
> suppressif 8|8 == 0x8;
>
> text
>
> help = STRING_TOKEN(STR_BITWISE_OR_HELP),
>
> text = STRING_TOKEN(STR_BITWISE_OR_PROMPT);
>
> endif;
>
>
>
> The equivalent 8&8 == 0x8 has no problem.
I must disagree. In the C language, both operator & and operator | bind
*less* strongly than operator ==. In 6.5 Expressions p3 it says
The grouping of operators and operands is indicated by the syntax.
(footnote 74). [...]
Footnote 74 says
The syntax specifies the precedence of operators in the evaluation of
an expression, which is the same as the order of the major subclauses
of this subclause, highest precedence first. [...]
And
6.5.9 Equality operators
Syntax
1 equality-expression:
relational-expression
equality-expression == relational-expression
equality-expression != relational-expression
[...]
6.5.10 Bitwise AND operator
Syntax
1 AND-expression:
equality-expression
AND-expression & equality-expression
Hence "equality-expression" is a stronger binding than "AND-expression".
Then,
6.5.11 Bitwise exclusive OR operator
Syntax
1 exclusive-OR-expression:
AND-expression
exclusive-OR-expression ^ AND-expression
[...]
6.5.12 Bitwise inclusive OR operator
Syntax
1 inclusive-OR-expression:
exclusive-OR-expression
inclusive-OR-expression | exclusive-OR-expression
Hence "equality-expression" is a stronger binding than
"inclusive-OR-expression", transitively, via "AND-expression" and
"exclusive-OR-expression".
So, at least in C (not sure about the VFR language),
8|8 == 0x8
means
8|(8 == 0x8)
means
8|1
means
9
This compares unequal to zero, so in a "truth" context, it means "true".
As I understand, you don't see that (ie. even though the binding is
different from what you assumed, the end result should coincide with
your expectation, but it doesn't happen.)
Maybe there's a bug in the form engine that uses "== 1" rather than "!=
0" for truth checks.
Then,
8&8 == 0x8
means
8&(8 == 0x8)
means
8&1
means
0
which is "false" (independently of whether the form engine otherwise
uses the correct "!= 0" form, or the incorrect "== 1" form).
Thanks
Laszlo
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