( Actions

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 8 Actions
 Each pattern in a rule has a corresponding "action", which can be any
 arbitrary C statement.  The pattern ends at the first non-escaped
 whitespace character; the remainder of the line is its action.  If the
 action is empty, then when the pattern is matched the input token is
 simply discarded.  For example, here is the specification for a program
 which deletes all occurrences of `zap me' from its input:
          "zap me"
    This example will copy all other characters in the input to the
 output since they will be matched by the default rule.
    Here is a program which compresses multiple blanks and tabs down to a
 single blank, and throws away whitespace found at the end of a line:
          [ \t]+        putchar( ' ' );
          [ \t]+$       /* ignore this token */
    If the action contains a `{', then the action spans till the
 balancing `}' is found, and the action may cross multiple lines.
 `flex' knows about C strings and comments and won't be fooled by braces
 found within them, but also allows actions to begin with `%{' and will
 consider the action to be all the text up to the next `%}' (regardless
 of ordinary braces inside the action).
    An action consisting solely of a vertical bar (`|') means "same as
 the action for the next rule".  See below for an illustration.
    Actions can include arbitrary C code, including `return' statements
 to return a value to whatever routine called `yylex()'.  Each time
 `yylex()' is called it continues processing tokens from where it last
 left off until it either reaches the end of the file or executes a
    Actions are free to modify `yytext' except for lengthening it
 (adding characters to its end-these will overwrite later characters in
 the input stream).  This however does not apply when using `%array'
 ( Matching). In that case, `yytext' may be freely modified in
 any way.
    Actions are free to modify `yyleng' except they should not do so if
 the action also includes use of `yymore()' (see below).
    There are a number of special directives which can be included
 within an action:
      copies yytext to the scanner's output.
      followed by the name of a start condition places the scanner in the
      corresponding start condition (see below).
      directs the scanner to proceed on to the "second best" rule which
      matched the input (or a prefix of the input).  The rule is chosen
      as described above in  Matching, and `yytext' and `yyleng'
      set up appropriately.  It may either be one which matched as much
      text as the originally chosen rule but came later in the `flex'
      input file, or one which matched less text.  For example, the
      following will both count the words in the input and call the
      routine `special()' whenever `frob' is seen:
                       int word_count = 0;
               frob        special(); REJECT;
               [^ \t\n]+   ++word_count;
      Without the `REJECT', any occurrences of `frob' in the input would
      not be counted as words, since the scanner normally executes only
      one action per token.  Multiple uses of `REJECT' are allowed, each
      one finding the next best choice to the currently active rule.  For
      example, when the following scanner scans the token `abcd', it will
      write `abcdabcaba' to the output:
               a        |
               ab       |
               abc      |
               abcd     ECHO; REJECT;
               .|\n     /* eat up any unmatched character */
      The first three rules share the fourth's action since they use the
      special `|' action.
      `REJECT' is a particularly expensive feature in terms of scanner
      performance; if it is used in _any_ of the scanner's actions it
      will slow down _all_ of the scanner's matching.  Furthermore,
      `REJECT' cannot be used with the `-Cf' or `-CF' options (
      Scanner Options).
      Note also that unlike the other special actions, `REJECT' is a
      _branch_.  Code immediately following it in the action will _not_
      be executed.
      tells the scanner that the next time it matches a rule, the
      corresponding token should be _appended_ onto the current value of
      `yytext' rather than replacing it.  For example, given the input
      `mega-kludge' the following will write `mega-mega-kludge' to the
               mega-    ECHO; yymore();
               kludge   ECHO;
      First `mega-' is matched and echoed to the output.  Then `kludge'
      is matched, but the previous `mega-' is still hanging around at the
      beginning of `yytext' so the `ECHO' for the `kludge' rule will
      actually write `mega-kludge'.
    Two notes regarding use of `yymore()'.  First, `yymore()' depends on
 the value of `yyleng' correctly reflecting the size of the current
 token, so you must not modify `yyleng' if you are using `yymore()'.
 Second, the presence of `yymore()' in the scanner's action entails a
 minor performance penalty in the scanner's matching speed.
    `yyless(n)' returns all but the first `n' characters of the current
 token back to the input stream, where they will be rescanned when the
 scanner looks for the next match.  `yytext' and `yyleng' are adjusted
 appropriately (e.g., `yyleng' will now be equal to `n').  For example,
 on the input `foobar' the following will write out `foobarbar':
          foobar    ECHO; yyless(3);
          [a-z]+    ECHO;
    An argument of 0 to `yyless()' will cause the entire current input
 string to be scanned again.  Unless you've changed how the scanner will
 subsequently process its input (using `BEGIN', for example), this will
 result in an endless loop.
    Note that `yyless()' is a macro and can only be used in the flex
 input file, not from other source files.
    `unput(c)' puts the character `c' back onto the input stream.  It
 will be the next character scanned.  The following action will take the
 current token and cause it to be rescanned enclosed in parentheses.
          int i;
          /* Copy yytext because unput() trashes yytext */
          char *yycopy = strdup( yytext );
          unput( ')' );
          for ( i = yyleng - 1; i >= 0; --i )
              unput( yycopy[i] );
          unput( '(' );
          free( yycopy );
    Note that since each `unput()' puts the given character back at the
 _beginning_ of the input stream, pushing back strings must be done
    An important potential problem when using `unput()' is that if you
 are using `%pointer' (the default), a call to `unput()' _destroys_ the
 contents of `yytext', starting with its rightmost character and
 devouring one character to the left with each call.  If you need the
 value of `yytext' preserved after a call to `unput()' (as in the above
 example), you must either first copy it elsewhere, or build your
 scanner using `%array' instead ( Matching).
    Finally, note that you cannot put back `EOF' to attempt to mark the
 input stream with an end-of-file.
    `input()' reads the next character from the input stream.  For
 example, the following is one way to eat up C comments:
          "/*"        {
                      register int c;
                      for ( ; ; )
                          while ( (c = input()) != '*' &&
                                  c != EOF )
                              ;    /* eat up text of comment */
                          if ( c == '*' )
                              while ( (c = input()) == '*' )
                              if ( c == '/' )
                                  break;    /* found the end */
                          if ( c == EOF )
                              error( "EOF in comment" );
    (Note that if the scanner is compiled using `C++', then `input()' is
 instead referred to as yyinput(), in order to avoid a name clash with
 the `C++' stream by the name of `input'.)
    `YY_FLUSH_BUFFER()' flushes the scanner's internal buffer so that
 the next time the scanner attempts to match a token, it will first
 refill the buffer using `YY_INPUT()' ( Generated Scanner).  This
 action is a special case of the more general `yy_flush_buffer()'
 function, described below ( Multiple Input Buffers)
    `yyterminate()' can be used in lieu of a return statement in an
 action.  It terminates the scanner and returns a 0 to the scanner's
 caller, indicating "all done".  By default, `yyterminate()' is also
 called when an end-of-file is encountered.  It is a macro and may be
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