.\" DO NOT MODIFY THIS FILE!  It was generated by help2man 1.23.
.TH GPERF "1" "April 2025" "GNU gperf 3.2.1" FSF
.SH NAME
gperf \- generate a perfect hash function from a key set
.SH SYNOPSIS
.B gperf
[\fIOPTION\fR]... [\fIINPUT-FILE\fR]
.SH DESCRIPTION
GNU 'gperf' generates perfect hash functions.
.PP
If a long option shows an argument as mandatory, then it is mandatory
for the equivalent short option also.
.SS "Output file location:"
.HP
\fB\-\-output\-file\fR=\fIFILE\fR Write output to specified file.
.PP
The results are written to standard output if no output file is specified
or if it is -.
.SS "Input file interpretation:"
.TP
\fB\-e\fR, \fB\-\-delimiters\fR=\fIDELIMITER\-LIST\fR
Allow user to provide a string containing delimiters
used to separate keywords from their attributes.
Default is ",".
.TP
\fB\-t\fR, \fB\-\-struct\-type\fR
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.
.TP
\fB\-\-ignore\-case\fR
Consider upper and lower case ASCII characters as
equivalent. Note that locale dependent case mappings
are ignored.
.SS "Language for the output code:"
.TP
\fB\-L\fR, \fB\-\-language\fR=\fILANGUAGE\-NAME\fR
Generates code in the specified language. Languages
handled are currently C++, ANSI-C, C, and KR-C. The
default is ANSI-C.
.SS "Details in the output code:"
.TP
\fB\-K\fR, \fB\-\-slot\-name\fR=\fINAME\fR
Select name of the keyword component in the keyword
structure.
.TP
\fB\-F\fR, \fB\-\-initializer\-suffix\fR=\fIINITIALIZERS\fR
Initializers for additional components in the keyword
structure.
.TP
\fB\-H\fR, \fB\-\-hash\-function\-name\fR=\fINAME\fR
Specify name of generated hash function. Default is
\&'hash'.
.TP
\fB\-N\fR, \fB\-\-lookup\-function\-name\fR=\fINAME\fR
Specify name of generated lookup function. Default
name is 'in_word_set'.
.TP
\fB\-Z\fR, \fB\-\-class\-name\fR=\fINAME\fR
Specify name of generated C++ class. Default name is
\&'Perfect_Hash'.
.TP
\fB\-7\fR, \fB\-\-seven\-bit\fR
Assume 7-bit characters.
.TP
\fB\-l\fR, \fB\-\-compare\-lengths\fR
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.
.TP
\fB\-c\fR, \fB\-\-compare\-strncmp\fR
Generate comparison code using strncmp rather than
strcmp.
.TP
\fB\-C\fR, \fB\-\-readonly\-tables\fR
Make the contents of generated lookup tables
constant, i.e., readonly.
.TP
\fB\-E\fR, \fB\-\-enum\fR
Define constant values using an enum local to the
lookup function rather than with defines.
.TP
\fB\-I\fR, \fB\-\-includes\fR
Include the necessary system include file <string.h>
at the beginning of the code.
.TP
\fB\-G\fR, \fB\-\-global\-table\fR
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).
.TP
\fB\-P\fR, \fB\-\-pic\fR
Optimize the generated table for inclusion in shared
libraries.  This reduces the startup time of programs
using a shared library containing the generated code.
.TP
\fB\-Q\fR, \fB\-\-string\-pool\-name\fR=\fINAME\fR
Specify name of string pool generated by option \fB\-\-pic\fR.
Default name is 'stringpool'.
.TP
\fB\-\-null\-strings\fR
Use NULL strings instead of empty strings for empty
keyword table entries.
.TP
\fB\-\-constants\-prefix\fR=\fIPREFIX\fR
Specify prefix for the constants like TOTAL_KEYWORDS.
.TP
\fB\-W\fR, \fB\-\-word\-array\-name\fR=\fINAME\fR
Specify name of word list array. Default name is
\&'wordlist'.
.TP
\fB\-\-length\-table\-name\fR=\fINAME\fR
Specify name of length table array. Default name is
\&'lengthtable'.
.TP
\fB\-S\fR, \fB\-\-switch\fR=\fICOUNT\fR
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.
.TP
\fB\-T\fR, \fB\-\-omit\-struct\-type\fR
Prevents the transfer of the type declaration to the
output file. Use this option if the type is already
defined elsewhere.
.SS "Algorithm employed by gperf:"
.TP
\fB\-k\fR, \fB\-\-key\-positions\fR=\fIKEYS\fR
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.
.TP
\fB\-D\fR, \fB\-\-duplicates\fR
Handle keywords that hash to duplicate values. This
is useful for certain highly redundant keyword sets.
.TP
\fB\-m\fR, \fB\-\-multiple\-iterations\fR=\fIITERATIONS\fR
Perform multiple choices of the \fB\-i\fR and \fB\-j\fR 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.
.TP
\fB\-i\fR, \fB\-\-initial\-asso\fR=\fIN\fR
Provide an initial value for the associate values
array. Default is 0. Setting this value larger helps
inflate the size of the final table.
.TP
\fB\-j\fR, \fB\-\-jump\fR=\fIJUMP\-VALUE\fR
Affects the "jump value", i.e., how far to advance
the associated character value upon collisions. Must
be an odd number, default is 5.
.TP
\fB\-n\fR, \fB\-\-no\-strlen\fR
Do not include the length of the keyword when
computing the hash function.
.TP
\fB\-r\fR, \fB\-\-random\fR
Utilizes randomness to initialize the associated
values table.
.TP
\fB\-s\fR, \fB\-\-size\-multiple\fR=\fIN\fR
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.
.SS "Informative output:"
.TP
\fB\-h\fR, \fB\-\-help\fR
Print this message.
.TP
\fB\-v\fR, \fB\-\-version\fR
Print the gperf version number.
.TP
\fB\-d\fR, \fB\-\-debug\fR
Enables the debugging option (produces verbose
output to the standard error).
.SH AUTHOR
Written by Douglas C. Schmidt and Bruno Haible.
.SH "REPORTING BUGS"
Report bugs to <bug-gperf@gnu.org>.
.SH COPYRIGHT
Copyright \(co 2025 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
.br
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
.SH "SEE ALSO"
The full documentation for
.B gperf
is maintained as a Texinfo manual.  If the
.B info
and
.B gperf
programs are properly installed at your site, the command
.IP
.B info gperf
.PP
should give you access to the complete manual.