Wrong #defined calculated value

Wrong #defined calculated value - Printable Version

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Wrong #defined calculated value - programandala.net - 06-21-2010

I think there's something I'm missing about the way #define values are calculated, look:

Code:
#define screenFirstCol 0

#define screenLastCol 31

#define borderFirstCol screenFirstCol

#define borderLastCol screenLastCol

#define oWinFirstCol  borderFirstCol+1

#define oWinLastCol borderLastCol-1

' Wrong result, 32 instead of 30:

#define oWinWidth oWinLastCol-oWinFirstCol+1

cls

print "Expected values in cramps:"

print

print "screenFirstCol(0)=";screenFirstCol

print "screenLastCol(31)=";screenLastCol

print "borderFirstCol(0)=";borderFirstCol

print "borderLastCol(31)=";borderLastCol

print "oWinFirstCol(1)=";oWinFirstCol

print "oWinLastCol(30)=";oWinLastCol

' Wrong result, 32 instead of 30:

print "oWinWidth(30)=";oWinWidth

pause 0

stop

What's the problem?

I think #defined values are simple labels calculated by the preprocessor. Is it right? Is there any limit about the depth of the calculated values?

Re: Wrong #defined calculated value - britlion - 06-22-2010

Not sure what's going on there. I get the same result.

It can't be because it's three things -

Code:
#define test 1+2+3

print test

comes back with 6, correctly.

The ic basically shows "print 32" as that last line that should be 30, so I can't easily drill down any further - the preprocessor is definitely making that set into a 32 though.

Re: Wrong #defined calculated value - boriel - 06-22-2010

programandala.net Wrote:I think there's something I'm missing about the way #define values are calculated, look:

Code:
#define screenFirstCol 0 #define screenLastCol 31 #define borderFirstCol screenFirstCol #define borderLastCol screenLastCol #define oWinFirstCol borderFirstCol+1 #define oWinLastCol borderLastCol-1 ' Wrong result, 32 instead of 30: #define oWinWidth oWinLastCol-oWinFirstCol+1

Let me check it:

borderFirstCol == 0
borderLasCol == 31
oWinFirstCol == 0 + 1 // Note: always expanded
oWinLastCol == 31 - 1
oWinWidth == 31 - 1 - 0 + 1 + 1 // This is the defined result

So oWinWidth == 32
Try using parenthesis in the #defines. The preprocessor does not calculate, just replace labels with code. With parenthesis:

Code:
#define screenFirstCol 0

#define screenLastCol 31

#define borderFirstCol screenFirstCol

#define borderLastCol screenLastCol

#define oWinFirstCol  (borderFirstCol+1)

#define oWinLastCol (borderLastCol-1)

' Wrong result, 32 instead of 30:

#define oWinWidth (oWinLastCol-oWinFirstCol+1)

This gives oWinWidth == ((31 - 1) - (0 + 1) + 1) which effectively is reduced to 30.
This also happens in C.

Quote:I think #defined values are simple labels calculated by the preprocessor. Is it right? Is there any limit about the depth of the calculated values?

No limit (only available memory).

Re: Wrong #defined calculated value - programandala.net - 06-22-2010

boriel Wrote:The preprocessor does not calculate, just replace labels with code. With parenthesis:

I see. The label is not replaced by the calculation, but by its raw content. Thank you.