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<HTML>
<HEAD>
<!-- This HTML file has been created by texi2html 1.51
from gperf.texi on 26 September 2000 -->
<TITLE>Perfect Hash Function Generator - 4 Invoking gperf</TITLE>
</HEAD>
<BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_5.html">previous</A>, <A HREF="gperf_7.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
<P><HR><P>
<H1><A NAME="SEC14" HREF="gperf_toc.html#TOC14">4 Invoking <CODE>gperf</CODE></A></H1>
<P>
There are <EM>many</EM> options to <CODE>gperf</CODE>. They were added to make
the program more convenient for use with real applications. "On-line"
help is readily available via the <SAMP>`-h'</SAMP> option. Here is the
complete list of options.
</P>
<H2><A NAME="SEC15" HREF="gperf_toc.html#TOC15">4.1 Options that affect Interpretation of the Input File</A></H2>
<DL COMPACT>
<DT><SAMP>`-e <VAR>keyword-delimiter-list</VAR>'</SAMP>
<DD>
<DT><SAMP>`--delimiters=<VAR>keyword-delimiter-list</VAR>'</SAMP>
<DD>
<A NAME="IDX16"></A>
Allows the user to provide a string containing delimiters used to
separate keywords from their attributes. The default is ",\n". This
option is essential if you want to use keywords that have embedded
commas or newlines. One useful trick is to use -e'TAB', where TAB is
the literal tab character.
<DT><SAMP>`-t'</SAMP>
<DD>
<DT><SAMP>`--struct-type'</SAMP>
<DD>
Allows you to include a <CODE>struct</CODE> type declaration for generated
code. Any text before a pair of consecutive <SAMP>`%%'</SAMP> is considered
part of the type declaration. Keywords and additional fields may follow
this, one group of fields per line. A set of examples for generating
perfect hash tables and functions for Ada, C, C++, Pascal, Modula 2,
Modula 3 and JavaScript reserved words are distributed with this release.
</DL>
<H2><A NAME="SEC16" HREF="gperf_toc.html#TOC16">4.2 Options to specify the Language for the Output Code</A></H2>
<DL COMPACT>
<DT><SAMP>`-L <VAR>generated-language-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--language=<VAR>generated-language-name</VAR>'</SAMP>
<DD>
Instructs <CODE>gperf</CODE> to generate code in the language specified by the
option's argument. Languages handled are currently:
<DL COMPACT>
<DT><SAMP>`KR-C'</SAMP>
<DD>
Old-style K&R C. This language is understood by old-style C compilers and
ANSI C compilers, but ANSI C compilers may flag warnings (or even errors)
because of lacking <SAMP>`const'</SAMP>.
<DT><SAMP>`C'</SAMP>
<DD>
Common C. This language is understood by ANSI C compilers, and also by
old-style C compilers, provided that you <CODE>#define const</CODE> to empty
for compilers which don't know about this keyword.
<DT><SAMP>`ANSI-C'</SAMP>
<DD>
ANSI C. This language is understood by ANSI C compilers and C++ compilers.
<DT><SAMP>`C++'</SAMP>
<DD>
C++. This language is understood by C++ compilers.
</DL>
The default is C.
<DT><SAMP>`-a'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
<DT><SAMP>`-g'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
</DL>
<H2><A NAME="SEC17" HREF="gperf_toc.html#TOC17">4.3 Options for fine tuning Details in the Output Code</A></H2>
<DL COMPACT>
<DT><SAMP>`-K <VAR>key-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--slot-name=<VAR>key-name</VAR>'</SAMP>
<DD>
<A NAME="IDX17"></A>
This option is only useful when option <SAMP>`-t'</SAMP> has been given.
By default, the program assumes the structure component identifier for
the keyword is <SAMP>`name'</SAMP>. This option allows an arbitrary choice of
identifier for this component, although it still must occur as the first
field in your supplied <CODE>struct</CODE>.
<DT><SAMP>`-F <VAR>initializers</VAR>'</SAMP>
<DD>
<DT><SAMP>`--initializer-suffix=<VAR>initializers</VAR>'</SAMP>
<DD>
<A NAME="IDX18"></A>
This option is only useful when option <SAMP>`-t'</SAMP> has been given.
It permits to specify initializers for the structure members following
<VAR>key name</VAR> in empty hash table entries. The list of initializers
should start with a comma. By default, the emitted code will
zero-initialize structure members following <VAR>key name</VAR>.
<DT><SAMP>`-H <VAR>hash-function-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--hash-fn-name=<VAR>hash-function-name</VAR>'</SAMP>
<DD>
Allows you to specify the name for the generated hash function. Default
name is <SAMP>`hash'</SAMP>. This option permits the use of two hash tables in
the same file.
<DT><SAMP>`-N <VAR>lookup-function-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--lookup-fn-name=<VAR>lookup-function-name</VAR>'</SAMP>
<DD>
Allows you to specify the name for the generated lookup function.
Default name is <SAMP>`in_word_set'</SAMP>. This option permits completely
automatic generation of perfect hash functions, especially when multiple
generated hash functions are used in the same application.
<DT><SAMP>`-Z <VAR>class-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--class-name=<VAR>class-name</VAR>'</SAMP>
<DD>
<A NAME="IDX19"></A>
This option is only useful when option <SAMP>`-L C++'</SAMP> has been given. It
allows you to specify the name of generated C++ class. Default name is
<CODE>Perfect_Hash</CODE>.
<DT><SAMP>`-7'</SAMP>
<DD>
<DT><SAMP>`--seven-bit'</SAMP>
<DD>
This option specifies that all strings that will be passed as arguments
to the generated hash function and the generated lookup function will
solely consist of 7-bit ASCII characters (characters in the range 0..127).
(Note that the ANSI C functions <CODE>isalnum</CODE> and <CODE>isgraph</CODE> do
<EM>not</EM> guarantee that a character is in this range. Only an explicit
test like <SAMP>`c >= 'A' && c <= 'Z''</SAMP> guarantees this.) This was the
default in versions of <CODE>gperf</CODE> earlier than 2.7; now the default is
to assume 8-bit characters.
<DT><SAMP>`-c'</SAMP>
<DD>
<DT><SAMP>`--compare-strncmp'</SAMP>
<DD>
Generates C code that uses the <CODE>strncmp</CODE> function to perform
string comparisons. The default action is to use <CODE>strcmp</CODE>.
<DT><SAMP>`-C'</SAMP>
<DD>
<DT><SAMP>`--readonly-tables'</SAMP>
<DD>
Makes the contents of all generated lookup tables constant, i.e.,
"readonly". Many compilers can generate more efficient code for this
by putting the tables in readonly memory.
<DT><SAMP>`-E'</SAMP>
<DD>
<DT><SAMP>`--enum'</SAMP>
<DD>
Define constant values using an enum local to the lookup function rather
than with #defines. This also means that different lookup functions can
reside in the same file. Thanks to James Clark <CODE><jjc@ai.mit.edu></CODE>.
<DT><SAMP>`-I'</SAMP>
<DD>
<DT><SAMP>`--includes'</SAMP>
<DD>
Include the necessary system include file, <CODE><string.h></CODE>, at the
beginning of the code. By default, this is not done; the user must
include this header file himself to allow compilation of the code.
<DT><SAMP>`-G'</SAMP>
<DD>
<DT><SAMP>`--global'</SAMP>
<DD>
Generate the static table of keywords as a static global variable,
rather than hiding it inside of the lookup function (which is the
default behavior).
<DT><SAMP>`-W <VAR>hash-table-array-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--word-array-name=<VAR>hash-table-array-name</VAR>'</SAMP>
<DD>
<A NAME="IDX20"></A>
Allows you to specify the name for the generated array containing the
hash table. Default name is <SAMP>`wordlist'</SAMP>. This option permits the
use of two hash tables in the same file, even when the option <SAMP>`-G'</SAMP>
is given.
<DT><SAMP>`-S <VAR>total-switch-statements</VAR>'</SAMP>
<DD>
<DT><SAMP>`--switch=<VAR>total-switch-statements</VAR>'</SAMP>
<DD>
<A NAME="IDX21"></A>
Causes the generated C code to use a <CODE>switch</CODE> statement scheme,
rather than an array lookup table. This can lead to a reduction in both
time and space requirements for some keyfiles. The argument to this
option determines how many <CODE>switch</CODE> statements are generated. A
value of 1 generates 1 <CODE>switch</CODE> containing all the elements, a
value of 2 generates 2 tables with 1/2 the elements in each
<CODE>switch</CODE>, etc. This is useful since many C compilers cannot
correctly generate code for large <CODE>switch</CODE> statements. This option
was inspired in part by Keith Bostic's original C program.
<DT><SAMP>`-T'</SAMP>
<DD>
<DT><SAMP>`--omit-struct-type'</SAMP>
<DD>
Prevents the transfer of the type declaration to the output file. Use
this option if the type is already defined elsewhere.
<DT><SAMP>`-p'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
</DL>
<H2><A NAME="SEC18" HREF="gperf_toc.html#TOC18">4.4 Options for changing the Algorithms employed by <CODE>gperf</CODE></A></H2>
<DL COMPACT>
<DT><SAMP>`-k <VAR>keys</VAR>'</SAMP>
<DD>
<DT><SAMP>`--key-positions=<VAR>keys</VAR>'</SAMP>
<DD>
Allows selection of the character key positions used in the keywords'
hash function. The allowable choices range between 1-126, inclusive.
The positions are separated by commas, e.g., <SAMP>`-k 9,4,13,14'</SAMP>;
ranges may be used, e.g., <SAMP>`-k 2-7'</SAMP>; and positions may occur
in any order. Furthermore, the meta-character '*' causes the generated
hash function to consider <STRONG>all</STRONG> character positions in each key,
whereas '$' instructs the hash function to use the "final character"
of a key (this is the only way to use a character position greater than
126, incidentally).
For instance, the option <SAMP>`-k 1,2,4,6-10,'$''</SAMP> generates a hash
function that considers positions 1,2,4,6,7,8,9,10, plus the last
character in each key (which may differ for each key, obviously). Keys
with length less than the indicated key positions work properly, since
selected key positions exceeding the key length are simply not
referenced in the hash function.
<DT><SAMP>`-l'</SAMP>
<DD>
<DT><SAMP>`--compare-strlen'</SAMP>
<DD>
Compare key lengths before trying a string comparison. This might cut
down on the number of string comparisons made during the lookup, since
keys with different lengths are never compared via <CODE>strcmp</CODE>.
However, using <SAMP>`-l'</SAMP> might greatly increase the size of the
generated C code if the lookup table range is large (which implies that
the switch option <SAMP>`-S'</SAMP> is not enabled), since the length table
contains as many elements as there are entries in the lookup table.
This option is mandatory for binary comparisons (see section <A HREF="gperf_5.html#SEC13">3.3 Use of NUL characters</A>).
<DT><SAMP>`-D'</SAMP>
<DD>
<DT><SAMP>`--duplicates'</SAMP>
<DD>
<A NAME="IDX22"></A>
Handle keywords whose key position sets hash to duplicate values.
Duplicate hash values occur for two reasons:
<UL>
<LI>
Since <CODE>gperf</CODE> does not backtrack it is possible for it to process
all your input keywords without finding a unique mapping for each word.
However, frequently only a very small number of duplicates occur, and
the majority of keys still require one probe into the table.
<LI>
Sometimes a set of keys may have the same names, but possess different
attributes. With the -D option <CODE>gperf</CODE> treats all these keys as
part of an equivalence class and generates a perfect hash function with
multiple comparisons for duplicate keys. It is up to you to completely
disambiguate the keywords by modifying the generated C code. However,
<CODE>gperf</CODE> helps you out by organizing the output.
</UL>
Option <SAMP>`-D'</SAMP> is extremely useful for certain large or highly
redundant keyword sets, e.g., assembler instruction opcodes.
Using this option usually means that the generated hash function is no
longer perfect. On the other hand, it permits <CODE>gperf</CODE> to work on
keyword sets that it otherwise could not handle.
<DT><SAMP>`-f <VAR>iteration-amount</VAR>'</SAMP>
<DD>
<DT><SAMP>`--fast=<VAR>iteration-amount</VAR>'</SAMP>
<DD>
Generate the perfect hash function "fast". This decreases
<CODE>gperf</CODE>'s running time at the cost of minimizing generated
table-size. The iteration amount represents the number of times to
iterate when resolving a collision. `0' means iterate by the number of
keywords. This option is probably most useful when used in conjunction
with options <SAMP>`-D'</SAMP> and/or <SAMP>`-S'</SAMP> for <EM>large</EM> keyword sets.
<DT><SAMP>`-i <VAR>initial-value</VAR>'</SAMP>
<DD>
<DT><SAMP>`--initial-asso=<VAR>initial-value</VAR>'</SAMP>
<DD>
Provides an initial <VAR>value</VAR> for the associate values array. Default
is 0. Increasing the initial value helps inflate the final table size,
possibly leading to more time efficient keyword lookups. Note that this
option is not particularly useful when <SAMP>`-S'</SAMP> is used. Also,
<SAMP>`-i'</SAMP> is overridden when the <SAMP>`-r'</SAMP> option is used.
<DT><SAMP>`-j <VAR>jump-value</VAR>'</SAMP>
<DD>
<DT><SAMP>`--jump=<VAR>jump-value</VAR>'</SAMP>
<DD>
<A NAME="IDX23"></A>
Affects the "jump value", i.e., how far to advance the associated
character value upon collisions. <VAR>Jump-value</VAR> is rounded up to an
odd number, the default is 5. If the <VAR>jump-value</VAR> is 0 <CODE>gperf</CODE>
jumps by random amounts.
<DT><SAMP>`-n'</SAMP>
<DD>
<DT><SAMP>`--no-strlen'</SAMP>
<DD>
Instructs the generator not to include the length of a keyword when
computing its hash value. This may save a few assembly instructions in
the generated lookup table.
<DT><SAMP>`-o'</SAMP>
<DD>
<DT><SAMP>`--occurrence-sort'</SAMP>
<DD>
Reorders the keywords by sorting the keywords so that frequently
occuring key position set components appear first. A second reordering
pass follows so that keys with "already determined values" are placed
towards the front of the keylist. This may decrease the time required
to generate a perfect hash function for many keyword sets, and also
produce more minimal perfect hash functions. The reason for this is
that the reordering helps prune the search time by handling inevitable
collisions early in the search process. On the other hand, if the
number of keywords is <EM>very</EM> large using <SAMP>`-o'</SAMP> may
<EM>increase</EM> <CODE>gperf</CODE>'s execution time, since collisions will
begin earlier and continue throughout the remainder of keyword
processing. See Cichelli's paper from the January 1980 Communications
of the ACM for details.
<DT><SAMP>`-r'</SAMP>
<DD>
<DT><SAMP>`--random'</SAMP>
<DD>
Utilizes randomness to initialize the associated values table. This
frequently generates solutions faster than using deterministic
initialization (which starts all associated values at 0). Furthermore,
using the randomization option generally increases the size of the
table. If <CODE>gperf</CODE> has difficultly with a certain keyword set try using
<SAMP>`-r'</SAMP> or <SAMP>`-D'</SAMP>.
<DT><SAMP>`-s <VAR>size-multiple</VAR>'</SAMP>
<DD>
<DT><SAMP>`--size-multiple=<VAR>size-multiple</VAR>'</SAMP>
<DD>
Affects the size of the generated hash table. The numeric argument for
this option indicates "how many times larger or smaller" the maximum
associated value range should be, in relationship to the number of keys.
If the <VAR>size-multiple</VAR> is negative the maximum associated value is
calculated by <EM>dividing</EM> it into the total number of keys. For
example, a value of 3 means "allow the maximum associated value to be
about 3 times larger than the number of input keys".
Conversely, a value of -3 means "allow the maximum associated value to
be about 3 times smaller than the number of input keys". Negative
values are useful for limiting the overall size of the generated hash
table, though this usually increases the number of duplicate hash
values.
If `generate switch' option <SAMP>`-S'</SAMP> is <EM>not</EM> enabled, the maximum
associated value influences the static array table size, and a larger
table should decrease the time required for an unsuccessful search, at
the expense of extra table space.
The default value is 1, thus the default maximum associated value about
the same size as the number of keys (for efficiency, the maximum
associated value is always rounded up to a power of 2). The actual
table size may vary somewhat, since this technique is essentially a
heuristic. In particular, setting this value too high slows down
<CODE>gperf</CODE>'s runtime, since it must search through a much larger range
of values. Judicious use of the <SAMP>`-f'</SAMP> option helps alleviate this
overhead, however.
</DL>
<H2><A NAME="SEC19" HREF="gperf_toc.html#TOC19">4.5 Informative Output</A></H2>
<DL COMPACT>
<DT><SAMP>`-h'</SAMP>
<DD>
<DT><SAMP>`--help'</SAMP>
<DD>
Prints a short summary on the meaning of each program option. Aborts
further program execution.
<DT><SAMP>`-v'</SAMP>
<DD>
<DT><SAMP>`--version'</SAMP>
<DD>
Prints out the current version number.
<DT><SAMP>`-d'</SAMP>
<DD>
<DT><SAMP>`--debug'</SAMP>
<DD>
Enables the debugging option. This produces verbose diagnostics to
"standard error" when <CODE>gperf</CODE> is executing. It is useful both for
maintaining the program and for determining whether a given set of
options is actually speeding up the search for a solution. Some useful
information is dumped at the end of the program when the <SAMP>`-d'</SAMP>
option is enabled.
</DL>
<P><HR><P>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_5.html">previous</A>, <A HREF="gperf_7.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
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