Info Catalog
flex: Yacc
flex: Top
flex: Performance
16 Scanner Options ****************** The various 'flex' options are categorized by function in the following menu. If you want to lookup a particular option by name, ⇒Index of Scanner Options.
· Options for Specifying Filenames
· Options Affecting Scanner Behavior
· Code-Level And API Options
· Options for Scanner Speed and Size
· Debugging Options
· Miscellaneous Options
Even though there are many scanner options, a typical scanner might
only specify the following options:
%option 8bit reentrant bison-bridge
%option warn nodefault
%option yylineno
%option outfile="scanner.c" header-file="scanner.h"
The first line specifies the general type of scanner we want. The
second line specifies that we are being careful. The third line asks
flex to track line numbers. The last line tells flex what to name the
files. (The options can be specified in any order. We just divided
them.)
'flex' also provides a mechanism for controlling options within the
scanner specification itself, rather than from the flex command-line.
This is done by including '%option' directives in the first section of
the scanner specification. You can specify multiple options with a
single '%option' directive, and multiple directives in the first section
of your flex input file.
Most options are given simply as names, optionally preceded by the
word 'no' (with no intervening whitespace) to negate their meaning. The
names are the same as their long-option equivalents (but without the
leading '--' ).
'flex' scans your rule actions to determine whether you use the
'REJECT' or 'yymore()' features. The 'REJECT' and 'yymore' options are
available to override its decision as to whether you use the options,
either by setting them (e.g., '%option reject)' to indicate the feature
is indeed used, or unsetting them to indicate it actually is not used
(e.g., '%option noyymore)'.
A number of options are available for lint purists who want to
suppress the appearance of unneeded routines in the generated scanner.
Each of the following, if unset (e.g., '%option nounput'), results in
the corresponding routine not appearing in the generated scanner:
input, unput
yy_push_state, yy_pop_state, yy_top_state
yy_scan_buffer, yy_scan_bytes, yy_scan_string
yyget_extra, yyset_extra, yyget_leng, yyget_text,
yyget_lineno, yyset_lineno, yyget_in, yyset_in,
yyget_out, yyset_out, yyget_lval, yyset_lval,
yyget_lloc, yyset_lloc, yyget_debug, yyset_debug
(though 'yy_push_state()' and friends won't appear anyway unless you
use '%option stack)'.