gperf(1)
NAME
gperf - generate a perfect hash function from a key set
SYNOPSIS
gperf [OPTION]... [INPUT-FILE]
DESCRIPTION
GNU 'gperf' generates perfect hash functions.
If a long option shows an argument as mandatory, then it is mandatory
for the equivalent short option also.
Output file location:
--output-file=FILE Write output to specified file.
The results are written to standard output if no output file is
specified or if it is -.
Input file interpretation:
-e, --delimiters=DELIMITER-LIST
Allow user to provide a string containing delimiters used to
separate keywords from their attributes. Default is ",".
-t, --struct-type
Allows the user to include a structured type declaration for
generated code. Any text before %% is considered part of the
type declaration. Key words and additional fields may follow
this, one group of fields per line.
--ignore-case
Consider upper and lower case ASCII characters as equivalent.
Note that locale dependent case mappings are ignored.
Language for the output code:
-L, --language=LANGUAGE-NAME
Generates code in the specified language. Languages handled are
currently C++, ANSI-C, C, and KR-C. The default is C.
Details in the output code:
-K, --slot-name=NAME
Select name of the keyword component in the keyword structure.
-F, --initializer-suffix=INITIALIZERS
Initializers for additional components in the keyword structure.
-H, --hash-function-name=NAME
Specify name of generated hash function. Default is 'hash'.
-N, --lookup-function-name=NAME
Specify name of generated lookup function. Default name is
'in_word_set'.
-Z, --class-name=NAME
Specify name of generated C++ class. Default name is
'Perfect_Hash'.
-7, --seven-bit
Assume 7-bit characters.
-l, --compare-lengths
Compare key lengths before trying a string comparison. This is
necessary if the keywords contain NUL bytes. It also helps cut
down on the number of string comparisons made during the lookup.
-c, --compare-strncmp
Generate comparison code using strncmp rather than strcmp.
-C, --readonly-tables
Make the contents of generated lookup tables constant, i.e.,
readonly.
-E, --enum
Define constant values using an enum local to the lookup
function rather than with defines.
-I, --includes
Include the necessary system include file <string.h> at the
beginning of the code.
-G, --global-table
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).
-P, --pic
Optimize the generated table for inclusion in shared libraries.
This reduces the startup time of programs using a shared library
containing the generated code.
-Q, --string-pool-name=NAME
Specify name of string pool generated by option --pic. Default
name is 'stringpool'.
--null-strings
Use NULL strings instead of empty strings for empty keyword
table entries.
-W, --word-array-name=NAME
Specify name of word list array. Default name is 'wordlist'.
--length-table-name=NAME
Specify name of length table array. Default name is
'lengthtable'.
-S, --switch=COUNT
Causes the generated C code to use a switch statement scheme,
rather than an array lookup table. This can lead to a reduction
in both time and space requirements for some keyfiles. The COUNT
argument determines how many switch statements are generated. A
value of 1 generates 1 switch containing all the elements, a
value of 2 generates 2 tables with 1/2 the elements in each
table, etc. If COUNT is very large, say 1000000, the generated C
code does a binary search.
-T, --omit-struct-type
Prevents the transfer of the type declaration to the output
file. Use this option if the type is already defined elsewhere.
Algorithm employed by gperf:
-k, --key-positions=KEYS
Select the key positions used in the hash function. The
allowable choices range between 1-255, inclusive. The positions
are separated by commas, ranges may be used, and key positions
may occur in any order. Also, the meta-character '*' causes the
generated hash function to consider ALL key positions, and $
indicates the "final character" of a key, e.g., $,1,2,4,6-10.
-D, --duplicates
Handle keywords that hash to duplicate values. This is useful
for certain highly redundant keyword sets.
-m, --multiple-iterations=ITERATIONS
Perform multiple choices of the -i and -j values, and choose the
best results. This increases the running time by a factor of
ITERATIONS but does a good job minimizing the generated table
size.
-i, --initial-asso=N
Provide an initial value for the associate values array. Default
is 0. Setting this value larger helps inflate the size of the
final table.
-j, --jump=JUMP-VALUE
Affects the "jump value", i.e., how far to advance the
associated character value upon collisions. Must be an odd
number, default is 5.
-n, --no-strlen
Do not include the length of the keyword when computing the hash
function.
-r, --random
Utilizes randomness to initialize the associated values table.
-s, --size-multiple=N
Affects the size of the generated hash table. The numeric
argument N indicates "how many times larger or smaller" the
associated value range should be, in relationship to the number
of keys, e.g. 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 1/3 means "make the maximum associated
value about 3 times smaller than the number of input keys". A
larger table should decrease the time required for an
unsuccessful search, at the expense of extra table space.
Default value is 1.
Informative output:
-h, --help
Print this message.
-v, --version
Print the gperf version number.
-d, --debug
Enables the debugging option (produces verbose output to the
standard error).
AUTHOR
Written by Douglas C. Schmidt and Bruno Haible.
REPORTING BUGS
Report bugs to <bug-gnu-gperf@gnu.org>.
COPYRIGHT
Copyright 1989-1998, 2000-2004, 2006-2007, 2009 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
The full documentation for gperf is maintained as a Texinfo manual. If
the info and gperf programs are properly installed at your site, the
command
info gperf
should give you access to the complete manual.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
