I am working on building a lexical and syntax analyzer. I am getting the following warning when I try to use flex with my .l file.
littleDuck.l:26: warning, rule cannot be matched
Rule 26 is the one that starts with {cteI}, my rules section is the following:
[ \t\n] ;
{RW} {return RESERVED;}
{id} {return ID;}
{ops} {return OPERATOR;}
{seps} {return SEPARATOR;}
{cteI} {yylval.ival = atoi(yytext); return INT;}
{cteF} {yylval.fval = atof(yytext); return FLOAT;}
{ctestring} {yylval.sval = strdup(yytext); return STRING;}
. ;
Also, my definitions section is this:
RW program|var|int|float|print|else|if
id ([a-z]|[A-Z)([a-z]|[A-Z]|[0-9])*
ops "="|"<"|">"|"<>"|"+"|"-"|"/"|"*"
seps ":"|","|";"|"{"|"}"|"("|")"
cteI [0-9]+
cteF {cteI}(\.{cteI}((e|E)("+"|"-")?{cteI})?)?
ctestring (\".*\")
Why is this warning appearing, and how can I modify my file so it will not appear?
The warning tells you that anything that might be matched by {cteI}
will always be matched by some earlier rule. In your case, it indicates that a rule doesn't match what you expect it does, probably due to a typo. In your case, its the {id}
rule, which you define as:
([a-z]|[A-Z)([a-z]|[A-Z]|[0-9])*
Notice the nesting of the parentheses and square brackets. Adding spaces for clarity, this is
( [a-z] | [A-Z)([a-z] | [A-Z] | [0-9] )*
This will match any sequence of letters, digits, or the characters (
)
or [
. You probably meant:
([a-z]|[A-Z])([a-z]|[A-Z]|[0-9])*
which can be more clearly written as
[a-zA-Z][a-zA-Z0-9]*