Manual

Chapter 10: C++ Language Interface 109
end position is advanced of its width. In case it matched ends of lines, the end cursor is
adjusted, and each time blanks are matched, the begin cursor is moved onto the end cursor
to effectively ignore the blanks preceding tokens. Comments would be treated equally.
%{
# define YY_USER_ACTION yylloc->columns (yyleng);
%}
%%
%{
yylloc->step ();
%}
{blank}+ yylloc->step ();
[\n]+ yylloc->lines (yyleng); yylloc->step ();
The rules are simple, just note the use of the driver to report errors. It is convenient to use
a typedef to shorten yy::calcxx_parser::token::identifier into token::identifier
for instance.
%{
typedef yy::calcxx_parser::token token;
%}
/* Convert ints to the actual type of tokens. */
[-+*/] return yy::calcxx_parser::token_type (yytext[0]);
":=" return token::ASSIGN;
{int} {
errno = 0;
long n = strtol (yytext, NULL, 10);
if (! (INT_MIN sval = new std::string (yytext); return token::IDENTIFIER;
. driver.error (*yylloc, "invalid character");
%%
Finally, because the scanner related driver’s member function depend on the scanner’s data,
it is simpler to implement them in this file.
void
calcxx_driver::scan_begin ()
{
yy_flex_debug = trace_scanning;
if (!(yyin = fopen (file.c_str (), "r")))
error (std::string ("cannot open ") + file);
}
void
calcxx_driver::scan_end ()
{
fclose (yyin);