flex options are categorized by function in the following
menu. If you want to lookup a particular option by name, See 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
%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
yymore() features. The
yymore options are available to override its decision as to
whether you use the options, either by setting them (e.g.,
reject) to indicate the feature is indeed used, or unsetting them to
indicate it actually is not used (e.g.,
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
yy_push_state() and friends won’t appear anyway unless