gcc gives warning: operation on 'variable' man be undefined 1

[flugh]

Greetings. First post to this forum.

Trying to compile this code on my Linux box using gcc 3.3.3. I get the following warning:
[tt]
gcc -Wall -O -ggdb -Dunix -DNOCRYPT bitsys.c -c -o obj/bitsys.o
bitsys.c: In function `str_flag_string':
bitsys.c:80: warning: operation on `toggle' may be undefined
[/tt]
The code in question is:
[tt]
75 char *str_flag_string(const struct flag_type *flag_table, FLAG * bits)
78 static int toggle;
79
80 toggle = (++toggle) % 10;
[/tt]
I'm really not sure how to fix the warning. Initializing it in the function will munge the static property right? The code compiles, but no warnings is a requirement. Any advice would be appreciated (slow replies though, I work a lot the first part of the week). By the way, it's some MUD code in case the context matters to anyone. I don't think that's important with this warning though.

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JBR

 

[ArkM]

You have ++ operation with side effect in your expression. Remember: x = y is an expression in C. Avoid such constructs because of C language does not define the moment of toggle value ++ modification. Split this expression statement if you want to write C Standard conformed code:

++toggle;
toggle %= 10;

 

[xwb]

Since toggle is a static, it will need an initial value.

char *str_flag_string...
{
   static int toggle = 0;
   toggle = (toggle + 1) % 10;

 

[ArkM]

All statics have initial value 0 by default in C/C++ (yes, it's a good style to initialize explicitly...

 

[flugh]

xwb: thanks. I avoided that explicit initialzation because it looks like there's some recursion involved and I didn't want to muck up that part up

ArkM: I split up the line like you suggested and it compiles without warning. I appreciate it!

I'm just working with C again after a couple years away. Trying to get a feel for someone else's code can be a booger, especially when you are old and rusty like me ;-)

----
JBR

 

[xwb]

Statics are special - they do not re-initialize on re-entry. They are only initialized once at the start of the program.

 

[lionelhill]

... they're basically a global variable that the compiler pretends is local.