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(flex.info)Miscellaneous

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Miscellaneous macros
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   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 below).  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' (see
Options below).  `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

   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.