Question about Lex

[Martin Weitzel]

In article <1991May29.081912.16808 at fel.tno.nl> gtir5 at fel.tno.nl (Ger Timmens) writes:
>This is what I do:
>
>1. lex lexcommands         /* ==> lex.yy.c */
>2. cc lex.yy.c             /* ==> a.out    */
>3. a.out < input > output  /* ==> output   */
>
>I've got the following problem:
>When I encounter a string in the file *input* I want to
>generate an error message reporting the line number and
>file.
>However I cannot include the following in my *lexcommands* file:
>
>"string"       fprintf(stderr,"Found *string* on line %d in %s.\n",
>                       __LINE__,__FILE__);
>
>since this would report the line number in the file *lex.yy.c* !

It's the purpose of the macros __LINE__ and __FILE__ to point you to the
source line - they don't have a meaning wrt the lines read at runtime.

If you have a 'plain vanilla' lex (as delivered with many UNIXes), there
might be an easy - yet undocumented - way: The standard input/unput-macros
support a variable 'yylino' which is incremented with every line read.

Of course, you can also build such a feature yourself by simply writing
a rule which recognices '\n' in the input and increments an arbitrary
variable.

>Is there a solution to this problem ?

Hope this helps.

>I've experimented with #line, but I did not succeed.

Also #line is not what you probably assume. It is meant to be used in
conjunction with __LINE__ and __FILE__ if your C source is generated from
some higher lever description. In this case #line sets the value of
__LINE__ and __FILE__ to point errors to the 'original' (higher level)
description.
-- 
Martin Weitzel, email: martin at mwtech.UUCP, voice: 49-(0)6151-6 56 83