The macro YY_USER_ACTION can be defined to provide an action which is always executed prior to the matched rule’s action. For example, it could be #define’d to call a routine to convert yytext to lower-case. When YY_USER_ACTION is invoked, the variable yy_act gives the number of the matched rule (rules are numbered starting with 1). Suppose you want to profile how often each of your rules is matched.
13 Miscellaneous Macros. The macro YY_USER_ACTION can be defined to provide an action which is always executed prior to the matched rule’s action. For example, it could be #define’d to call a routine to convert yytext to lower-case. When YY_USER_ACTION is invoked, the variable yy_act gives the number of the matched rule (rules are numbered starting …
The macro YY_USER_ACTION can be redefined to provide an action which is always executed prior to the matched rule’s action. For example, it could be #defined.
12/5/2016 · We can do this in the YY_USER_ACTION macro, which is called just before any lexer action is performed that ensures that if a rule matches but it doesn’t return a value (for instance, a rule skipping whitespace or comments), the location of that non-token is skipped, rather than being included at the beginning of the actual token, or lost in a way that makes the location tracking inaccurate.
Lexical Analysis With Flex, for Flex 2.6.3: Misc Macros, Using flex – Input and Output Files, Flex – a scanner generator – GNU, Flex – a scanner generator – GNU, Flex Actions. When a pattern is matched, the corresponding action is triggered. The actions default to nothing, i.e.
discard the current token. In the output, the actions are embedded in the yylex function, therefore, using return sets the return value of yylex. All the actions may use:, 6/21/2016 · Furthermore, there are three macros that can be used to set data and code inside the scanner, YY_USER_DATA() (not in regular flex), YY_USER_INIT(), and YY_USER_ACTION(). If you use these macros, you must put them in the block between %{and %}. See above, the basic scanner.
10/17/2015 · I’m using flex 2.5.35 and bison 2.7 (though this is a flex issue, I believe, so I’ve omitted parser.y) My Flex grammar is very simple: lexer.l. % { #define YY_NO_INPUT #include parser.h #define YY_USER_ACTION yylloc->first_line = yylloc->last_line = yylineno yylloc->first_column = yycolumn yylloc->last_column = yycolumn + (int)yyleng – 1 …
plus almost all of the flex flags. The last feature in the list refers to the fact that with flex you can put multiple actions on the same line, separated with semicolons, while with lex, the following foo handle_foo() ++num_foos_seen is (rather surprisingly) truncated to foo handle_foo() flex does not truncate the action. Actions that are not enclosed in braces are simply terminated at the end of the line.
An alternative solution is to count the number of characters you’ve matched since starting to scan. This can be done by using YY_USER_ACTION . For example, #define YY_USER_ACTION num_chars += yyleng (You need to be careful to update your bookkeeping if you use yymore ( …
