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15 Interfacing with Yacc
One of the main uses of flex
is as a companion to the yacc
parser-generator. yacc
parsers expect to call a routine named
yylex()
to find the next input token. The routine is supposed to
return the type of the next token as well as putting any associated
value in the global yylval
. To use flex
with yacc
,
one specifies the ‘-d’ option to yacc
to instruct it to
generate the file ‘y.tab.h’ containing definitions of all the
%tokens
appearing in the yacc
input. This file is then
included in the flex
scanner. For example, if one of the tokens
is TOK_NUMBER
, part of the scanner might look like:
%{ #include "y.tab.h" %} %% [0-9]+ yylval = atoi( yytext ); return TOK_NUMBER;
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