lex & yacc - cupla questions

[Tim Kuehn]

(Dave Astels) writes:
>woodward at uicbert.eecs.uic.edu writes:
>>3.)  if i have a yacc construct such as:
>> 
>>line3	: 	A B C
>>		{  yacc action sequence }
>>
>>how can i now assign the values of A, B, and C into local vars of my
>>choice?  the problem lies in the fact that each of A B and C represent
>>three calls to lex, and if i pass back a pointer to yytext[] from lex, 
>>i only retain the value of the last token in the sequence, in this case C, 
>>when i get to the action sequence in my yacc code.
>
>return a copy of yytext, not a pointer to it.

That still doesn't solve the problem as you don't know *which* rule has 
fired,  and where to store the text value associated with tokens A B C until 
after you've made three (or more) calls to yylex. However, provision for 
handling this in provided with the yylval, which can be used with the 
%union {} declaration in yacc, and assigned in the action associated with 
the regexp's in lex. In the case where text values associated with these 
tokens, one would include a char pointer declaration in the %union statement, 
(say char *cval) copy the text value to a malloc'd space, and assign 
the pointer to yylval.cval before returning from lex. This will be saved 
on the value stack yacc maintains as it goes through it's states, and can 
be retreived by making reference to $$, $1, $2, or $3 (the equivalent 
variable names for the rule, first, second, and third elements of the rule 
respectively). 

Check your yacc/lex manual for more details. 

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