pitfalls in flex 2.5.xx

[Bastian Kleineidam <calvin@debian.org>]

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Hi,

I've seen that a lot of release critical errors come from the new
flex 2.5.xx version in unstable.

Here are some of the more common pitfalls:

1) These strings are not allowed in any flex input files, not
   even in comments:  "m4_" "[[" "]]"
   So if you have x[i[j]] in your C code, flex will fail!

   Solution: dont use m4_ prefix and put a space between [[ and ]]
   see flex.info, node "M4 Dependency" for more info

2) yylineno is redefined (eg int yylineno = 0;)
   
   Solution: Rename this variable to something else, eg mylineno.
   Or use the internal line counting of flex with
   "%options yylineno" and "int lineno() const" for accessing.

3) yytext_ptr is undefined
   You use unput() after the second %% in your lexer file.
   This is not possible anymore due to a bug in flex.
   See http://bugs.debian.org/189332 for more info.

   Solution: move the unput() usage in the rules or header section
   (ie between or above the two %%).
   Or wait until the flex people fix this :)


Cheers, Bastian
- -- 

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