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troubleshooting Question

toupper() of 1 or 0

Avatar of Stephen Kairys
Stephen KairysFlag for United States of America asked on
C
9 Comments1 Solution435 ViewsLast Modified:
In parsing an arglist in a C program, I meant to say (to enable validation if
the arg in question had a 'V' or 'v' in the "2nd" positoin e.g. -XV or -xv

if (toupper(argv[argc-1][2]) == 'V') then
   do_validation = TRUE;

but I had a typo:

if (toupper(argv[argc -1][2] == 'V'))
   do_validation = TRUE;

so in effect I was taking toupper() not of 'V', 'v', or whatever, but of the entire
expression:

(argv[argc -1][2] == 'V')

As blatant as that typo was, I found that do_validation was still being set to TRUE
if the value in question was 'V' (but not 'v', or anything else) e.g.
-XV sets is to TRUE
-xv does not
-x does not
-X does not


I want to be sure I understand why. As I see it, if the char in question
argv[argc -1][2]
is 'V', then the expression:
(argv[argc -1][2] == 'V')
evaiuates to 1.
toupper(1) is (char)1.

For any other value, including NULL (which would be the case if I had -X)
(argv[argc -1][2] == 'V')
evaluates to 0
toupper(0) is (char)0.

Ergo, my test still works, as long as I have an UPPERCASE 'V' .
Of course, I will fix this, but as I may have some sites running -XV right now, I want to
rest assured they will be enabling the validation flag.

So...is my analysis correct?

Thanks,
Steve





ASKER CERTIFIED SOLUTION
Avatar of Peter Kwan
Peter KwanFlag of Hong Kong imageAnalyst Programmer

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