(flex.info.gz) Misc Macros

 
 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 with 1).
 Suppose you want to profile how often each of your rules is matched.
 The following would do the trick:
 
 
          #define YY_USER_ACTION ++ctr[yy_act]
 
    where `ctr' is an array to hold the counts for the different rules.
 Note that the macro `YY_NUM_RULES' gives the total number of rules
 (including the default rule), even if you use `-s)', so a correct
 declaration for `ctr' is:
 
 
          int ctr[YY_NUM_RULES];
 
    The macro `YY_USER_INIT' may be defined to provide an action which
 is always executed before the first scan (and before the scanner's
 internal initializations are done).  For example, it could be used to
 call a routine to read in a data table or open a logging file.
 
    The macro `yy_set_interactive(is_interactive)' can be used to
 control whether the current buffer is considered "interactive".  An
 interactive buffer is processed more slowly, but must be used when the
 scanner's input source is indeed interactive to avoid problems due to
 waiting to fill buffers (see the discussion of the `-I' flag in 
 Scanner Options).  A non-zero value in the macro invocation marks the
 buffer as interactive, a zero value as non-interactive.  Note that use
 of this macro overrides `%option always-interactive' or `%option
 never-interactive' ( Scanner Options).  `yy_set_interactive()'
 must be invoked prior to beginning to scan the buffer that is (or is
 not) to be considered interactive.
 
    The macro `yy_set_bol(at_bol)' can be used to control whether the
 current buffer's scanning context for the next token match is done as
 though at the beginning of a line.  A non-zero macro argument makes
 rules anchored with `^' active, while a zero argument makes `^' rules
 inactive.
 
    The macro `YY_AT_BOL()' returns true if the next token scanned from
 the current buffer will have `^' rules active, false otherwise.
 
    In the generated scanner, the actions are all gathered in one large
 switch statement and separated using `YY_BREAK', which may be
 redefined.  By default, it is simply a `break', to separate each rule's
 action from the following rule's.  Redefining `YY_BREAK' allows, for
 example, C++ users to #define YY_BREAK to do nothing (while being very
 careful that every rule ends with a `break' or a `return'!) to avoid
 suffering from unreachable statement warnings where because a rule's
 action ends with `return', the `YY_BREAK' is inaccessible.
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