Info Catalog flex: Format flex: Format flex: Rules Section

flex: Definitions Section

 
 5.1 Format of the Definitions Section
 =====================================
 
 The "definitions section" contains declarations of simple "name"
 definitions to simplify the scanner specification, and declarations of
 "start conditions", which are explained in a later section.
 
    Name definitions have the form:
 
          name definition
 
    The 'name' is a word beginning with a letter or an underscore ('_')
 followed by zero or more letters, digits, '_', or '-' (dash).  The
 definition is taken to begin at the first non-whitespace character
 following the name and continuing to the end of the line.  The
 definition can subsequently be referred to using '{name}', which will
 expand to '(definition)'.  For example,
 
          DIGIT    [0-9]
          ID       [a-z][a-z0-9]*
 
    Defines 'DIGIT' to be a regular expression which matches a single
 digit, and 'ID' to be a regular expression which matches a letter
 followed by zero-or-more letters-or-digits.  A subsequent reference to
 
          {DIGIT}+"."{DIGIT}*
 
    is identical to
 
          ([0-9])+"."([0-9])*
 
    and matches one-or-more digits followed by a '.' followed by
 zero-or-more digits.
 
    An unindented comment (i.e., a line beginning with '/*') is copied
 verbatim to the output up to the next '*/'.
 
    Any _indented_ text or text enclosed in '%{' and '%}' is also copied
 verbatim to the output (with the %{ and %} symbols removed).  The %{ and
 %} symbols must appear unindented on lines by themselves.
 
    A '%top' block is similar to a '%{' ...  '%}' block, except that the
 code in a '%top' block is relocated to the _top_ of the generated file,
 before any flex definitions (1).  The '%top' block is useful when you
 want certain preprocessor macros to be defined or certain files to be
 included before the generated code.  The single characters, '{' and '}'
 are used to delimit the '%top' block, as show in the example below:
 
          %top{
              /* This code goes at the "top" of the generated file. */
              #include <stdint.h>
              #include <inttypes.h>
          }
 
    Multiple '%top' blocks are allowed, and their order is preserved.
 
    ---------- Footnotes ----------
 
    (1) Actually, 'yyIN_HEADER' is defined before the '%top' block.
 

Info Catalog flex: Format flex: Format flex: Rules Section