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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 (see section 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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