FB II COMPILER
Comprehend the % symbol
<< _resPurgeable = 5
Often, i see _resPurgeable as _resPurgeable% (note the %)
Why ? >>
_resPurgeable% means: "2 raised to the power of _resPurgeable." Where _resPurgeable equals 5, _resPurgeable% equals 32.
The reason this is useful is that many predefined constants represent a bit position that's used in some binary number. If you have some constant _myBitPos defined, then _myBitPos% represents: "the binary number which has the bit in position _myBitPos set to 1, and all the other bits set to 0."
<< If i wanted to replace the constant with the numeral, should i use 5 or 5%??? >>
Either. While _resPurgeable and _resPurgeable% have two completely different values, 5 and 5% both mean 5. In _most_ cases, a symbolic constant and its literal equivalent are interchangeable, but this is an exception.
To make things even more confusing, if you use a symbolic constant following a "dot," then the "%" suffix means something else; namely "short integer." So:
_resPurgeable means 5
_resPurgeable% means 32
but:
myRecord.resPurgeable% means: "the short integer located 5 bytes past the beginning of myRecord". If "short-integer" is your default variable type, then "myRecord.resPurgeable%" is exactly identical to "myRecord.resPurgeable".
Note that you can also use the syntax _myConst% in situations where a symbolic constant or literal integer is required. So, while these all represent the same value:
_myConst%
BIT(_myConst)
2 ^ _myConst
...only the first of the following will compile:
DIM z(_myConst%) 'will compile
DIM z(BIT(_myConst)) 'won't compile
DIM z(2 ^ _myConst) 'won't compile
<< Also, if more than one constant is used, can i really only replace the whole thing with just the total value?
COMPILE 0, _pointerVars _appendRes _dimmedVarsOnly >>
Yes. The compiler sums all the constants. It gives the same result as the expression "_pointerVars + _appendRes + _dimmedVarsOnly", but the two forms are used in two different situations:
* You must _exclude_ the "+" symbol(s) in statement that require a symbolic constant or integer literal.
* You must _include_ the "+" symbol(s) in statements that _don't_ require a symbolic constant or literal integer.
So, these will compile:
_myConst = _k4 _k5
DIM myArray%(_k1 _k2 _k3)
...but these won't:
_myConst = _k4 + _k5
DIM myArray%(_k1+_k2+_k3)
Also, these will compile:
myNumber% = _k1 + _k2
PRINT _k3 + _k4
...but these won't:
myNumber% = _k1 _k2
PRINT _k3 _k4
Finally, the "space means '+'" syntax won't work for symbolic constants that have the "%" suffix, nor for literal integers.
This won't compile:
DIM myArray%(7 22)
This _will_ compile, but gives unpredictable results!
DIM myArray%(_k1% _k2%)
Rick