Hello,
just have started to write my first parser with flex and bison
and have run in a problem I cannot understand or solve myself.
So I would be really glad if somebody on this list would help me a bit
since I think the problem is caused by my limited understanding of
the internals of bison.
The problem is that whenever I pass a number token from flex to
bison in order to process it
the values of the variables $1 and $3 are different from the ones
passed by a similar string token.
For example:
# The number token is: "3 == 3"
--------------------------------
The rule in flex is:
NUMBER -?(([0-9]+)|([0-9]*\.[0-9]+))
EQUAL ==
;
{NUMBER} { yylval.num = atof(yytext); return NUMBER; }
{EQUAL} { return EQUAL; }
In bison:
num_expr: NUMBER EQUAL NUMBER { printf("EQUAL: 1: %f | 3: %f\n", $1,
$3); $$ = $1 == $3; }
# The string token is: "aa == bb"
----------------------------------
The rule in flex is:
WORD ([a-zA-Z]+)([0-9]*)|([0-9]+)([a-zA-Z]+)
EQUAL ==
;
{EQUAL} { return EQUAL; }
{WORD} { yylval.str = yytext; return WORD; }
In bison:
str_expr: WORD EQUAL WORD { printf( "EQUAL: 1: \"%s\" | 3: \"%s
\"\n", $1,$3 ); sprintf( $$, "%i", strcmp( $1, $3 ) ); }
Whenever I pass a number the variable $1 is filled with the first
NUMBER (in this case 3)
and the variable $3 is filled with the second NUMBER (also 3) in
bison as I expected
But when I pass the string token "aa == bb" the variable $1 is
filled with the *whole token* itself (in this case "aa == bb")
and not with the first WORD which would be "aa". The variable $3 is
filled with the second WORD (which is "bb") as expected.
Has anybody got a clue what happens here ?
Thanks in advance,
Arno
P.S.: I use bison 1.875c and flex 2.5.4 on Fedora Core release 3
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