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How can I customize my error message in yacc/lex project to display the line and type of problem?

I am new in programming but I have a yacc/lex project and some difficulty in writing the error message in detail (line and type of error). Any help with a small example, please.

Solution

  • Add the following to your flex scanner definition, to cause the scanner to track line numbers:

    %option yylineno

    (See the flex manual.)

    Then add the following declarations to your bison grammar:

    %define parse.error verbose
%define parse.lac full

    (See the bison manual chapters on error reporting and LAC (lookahead correction).

    Finally, use a definition of yyerror which uses the line number information. At a minimum, something like:

    void yyerror(const char* msg) {
  fprintf(stderr, "At line %d: %s\n", yylineno, msg);
}