--- name: "gperf" section: "1" platform: "linux" package: "gperf" version: "3.3-2" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/gperf" --- # gperf(1) generate a perfect hash function from a key set ## 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 ANSI-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 \ 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. - **--constants-prefix**=*PREFIX* Specify prefix for the constants like TOTAL\_KEYWORDS. - **-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 \. ## COPYRIGHT Copyright © 2025 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later \\ This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. ## 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.