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Lexer: Simple Flex Template

Posted 08-19-2017 at 03:16 AM by astrogeek

Flex / Bison Project Template, Flex lexer source file.

Save this source to a file named fbproject.l in the same directory as other project template files.

This file defines a Flex based lexer which along with the Bison parser source and Makefile will allow you to quickly build a working project template with the essential features required by many projects, as described in the project README file.

Code:

%{
/* Flex/Bison tutorial skeleton lexer definitions
        Robert Allen April 16, 2017
*/
/* Include Bison generated header to import tokens */
#include "fbproject.tab.h"

/* Using Bison locations so we define yycolumn and YY_USER_ACTION
to keep column count in sync on each pattern match */
int yycolumn=1;
#define YY_USER_ACTION yylloc.filename=filename; \
yylloc.first_line = yylloc.last_line = yylineno; \
yylloc.first_column = yycolumn; yylloc.last_column = yycolumn+yyleng-1; \
yycolumn += yyleng;
%}

%option header-file="fbproject.lex.h"
%option yylineno
        /*%option nodefault*/

 /* If not defining our own yywrap() compile with -lfl
    for default or enable option noyywrap, negate -lfl
%option noyywrap
 */

 /* We will define two types of comment:
 C-type multi-line
 Shell type where # is first character on line
 We handle C-type with an exclusive start state, COMMENT
 */
%x COMMENT

%%
 /* C-type multi-line comment */
"/*" {BEGIN(COMMENT);}
<COMMENT>{
"*/" {BEGIN(0);}
[^*\n]+
"*"[^/]
\n { yycolumn=1; }
<<EOF>> { lyyerror("%s: %i.%i: missing */: unclosed comment at end of file",yylloc.filename, yylineno, yylloc.first_column);
        return EOF; }
}
 /* Shell type comment */
^[ \t]*#.* {/* Do nothing*/ }

 /* Single line, double-quoted strings, strip quotes */
\"(\\.|\"\"|[^"\n])*\" { yylval.sval = strndup(yytext+1,yyleng-2); return QSTRING; }
\"(\\.|\"\"|[^"\n])*$  { lyyerror("%s: %i.%i: missing \": unclosed quote at end of line",yylloc.filename, yylineno, yylloc.first_column);
        yylval.sval = strndup(yytext+1,yyleng-1); return QSTRING; }

 /* Commands, keywords */
(?i:"q"|"qu"|"qui"|"quit") { return QUIT; }
(?i:"d"|"db"|"debug") { return DBG; }
(?i:"h"|"?"|"help") { return HELP; }

[ \t]+ {/*Eat up whitespace*/}
. { /* Anything else not recognized is an error
        This parser always recovers to EOL so we grab trailing non-sapce
        chars for user visual context */
        char buf[32] ={0};
        int i=0;
        buf[i]=yytext[i];
        for(i++;i<30;i++){
                buf[i]=input();
                if(buf[i]<'!' || buf[i] >'z'){
                        unput(buf[i]);
                        break;}
                yycolumn++;
                yylloc.last_column++;
        }
        lyyerror("%s: %i.%i-%i.%i: unrecognized input: %s", yylloc.filename, yylineno, yylloc.first_column, \
        yylineno, yylloc.last_column, buf);
        return ERRTOK; }

\n { yycolumn=1; return EOL; }

%%

Posted in Tutorials and Templates, Flex/Bison Project Template

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