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Full Discussion: Multiple scanners on same input file using lex/flex
Top Forums Programming Multiple scanners on same input file using lex/flex Post 302094135 by Rakesh Ranjan on Wednesday 25th of October 2006 02:06:15 PM
Old 10-25-2006
Question Multiple scanners on same input file using lex/flex
Hi all,

I'm working with flex (version 2.5.4a) on GNU/linux. I used it to develop 4 scanner C files for matching different patterns within an input file. But the problem now on my hand is that I need to conditionally combine these. That is in main (placed in a separate C file other than the 4 scanner files) I'll have check the options provided by the user and accordingly call the scanner functions from the scanner C files.
For ex. if main is in file app.c and options are:
-f - for scanner function of 1st scanner file
-s - for scanner function of 2nd scanner file
-t - for scanner function of 3rd scanner file
-r - for scanner function of 4th scanner file
so something like './app -f -s -r filename' would mean that the scanners from 1st, 2nd and 4th file are called while 3rd's is not called.

The problem with such a situation is that when lex is invoked it generates C file with scanner function yylex() (and supporting functions for it). Now this function has same signature in all 4 scanners and hence the inclusion of all 4 files causes name conflict ("error: yylex() redifned here". Even -P option does not help as it just #define s the original function).

Now I hope everybody must be understanding my difficulty. Is there any way out (without changing to C++)?
While I'll like a functional decomposition as stated above but even if someone can come up with a solution where I need to combine all lex files to one and still be able to control what pattern are to be matched according to the switch provided by user in 'main()' will be a great help.

Thanks in advance!
 

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LEARN ABOUT CENTOS

lex

FLEX(1) 							   User Commands							   FLEX(1)

NAME

       flex - the fast lexical analyser generator

SYNOPSIS

       flex [OPTIONS] [FILE]...

DESCRIPTION

       Generates programs that perform pattern-matching on text.

   Table Compression:
       -Ca, --align
	      trade off larger tables for better memory alignment

       -Ce, --ecs
	      construct equivalence classes

       -Cf    do not compress tables; use -f representation

       -CF    do not compress tables; use -F representation

       -Cm, --meta-ecs
	      construct meta-equivalence classes

       -Cr, --read
	      use read() instead of stdio for scanner input

       -f, --full
	      generate fast, large scanner. Same as -Cfr

       -F, --fast
	      use alternate table representation. Same as -CFr

       -Cem   default compression (same as --ecs --meta-ecs)

   Debugging:
       -d, --debug
	      enable debug mode in scanner

       -b, --backup
	      write backing-up information to lex.backup

       -p, --perf-report
	      write performance report to stderr

       -s, --nodefault
	      suppress default rule to ECHO unmatched text

       -T, --trace
	      flex should run in trace mode

       -w, --nowarn
	      do not generate warnings

       -v, --verbose
	      write summary of scanner statistics to stdout

   Files:
       -o, --outfile=FILE
	      specify output filename

       -S, --skel=FILE
	      specify skeleton file

       -t, --stdout
	      write scanner on stdout instead of lex.yy.c

       --yyclass=NAME
	      name of C++ class

       --header-file=FILE
	      create a C header file in addition to the scanner

       --tables-file[=FILE] write tables to FILE

   Scanner behavior:
       -7, --7bit
	      generate 7-bit scanner

       -8, --8bit
	      generate 8-bit scanner

       -B, --batch
	      generate batch scanner (opposite of -I)

       -i, --case-insensitive
	      ignore case in patterns

       -l, --lex-compat
	      maximal compatibility with original lex

       -X, --posix-compat
	      maximal compatibility with POSIX lex

       -I, --interactive
	      generate interactive scanner (opposite of -B)

       --yylineno
	      track line count in yylineno

   Generated code:
       -+,  --c++
	      generate C++ scanner class

       -Dmacro[=defn]
	      #define macro defn  (default defn is '1')

       -L,  --noline
	      suppress #line directives in scanner

       -P,  --prefix=STRING
	      use STRING as prefix instead of "yy"

       -R,  --reentrant
	      generate a reentrant C scanner

       --bison-bridge
	      scanner for bison pure parser.

       --bison-locations
	      include yylloc support.

       --stdinit
	      initialize yyin/yyout to stdin/stdout

       --noansi-definitions old-style function definitions

       --noansi-prototypes
	      empty parameter list in prototypes

       --nounistd
	      do not include <unistd.h>

       --noFUNCTION
	      do not generate a particular FUNCTION

   Miscellaneous:
       -c     do-nothing POSIX option

       -n     do-nothing POSIX option

       -?

       -h, --help
	      produce this help message

       -V, --version
	      report flex version

SEE ALSO

       The  full documentation for flex is maintained as a Texinfo manual.  If the info and flex programs are properly installed at your site, the
       command

	      info flex

       should give you access to the complete manual.

flex 2.5.36							     July 2012								   FLEX(1)
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