.\"   Part of publib.
.\"  
.\"   Copyright (c) 2012 Antti-Juhani Kaijanaho.
.\"   Copyright (c) 1994-2006 Lars Wirzenius.  All rights reserved.
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.TH HASH 3pub "C Programmer's Manual" "Publib" "C Programmer's Manual"
.SH NAME
hash_create, hash_destroy, hash_install, hash_lookup, hash_uninstall,
hash_iter \- generic hash tables
.SH SYNOPSIS
.nf
#include <publib.h>
.sp 1
Hashtab *\fBhash_create\fR(unsigned long (*\fIfun\fR)(void *),
         int (*\fIcmp\fR)(const void *, const void *));
void \fBhash_destroy\fR(Hashtab *\fIht\fR);
void *\fBhash_install\fR(Hashtab *\fIht\fR, void *\fIdata\fR, size_t \fIsize\fR);
void *\fBhash_lookup\fR(Hashtab *\fIht\fR, void *\fIdata\fR);
int \fBhash_uninstall\fR(Hashtab *\fIht\fR, void *\fIdata\fR);
int \fBhash_iter\fR(Hashtab *\fIht\fR, int (*\fIdoit\fR)(void *, void *), void *\fIparam\fR);
.SH "DESCRIPTION"
These functions implement generic hash tables.
The table is created by \fIhash_create\fR and destroyed by \fIhash_destroy\fR.
The \fIfun\fR argument is a pointer to the hashing function,
which must convert a datum to an unsigned long, which is then converted
to an index into the hashing table.
\fIcmp\fR is a \fIqsort\fR(3)-like comparison functions, used to compare
to (wannabe) hash table elements.
.PP
\fIhash_install\fR installs a new datum into the table.
A pointer to the data and the size of the data are given as the arguments.
If the size is 0, only the pointer value is copied to the table.
Otherwise a copy of the data is made into dynamically allocated memory.
.PP
\fIhash_lookup\fR attempts to find a datum in the hash table.
A pointer to another datum is given as the argument.
The comparison function should compare equal (return 0)
the desired datum and this datum (but the argument needn't be a fully
initialized datum, although that is up to the writer of the comparison
function).
There cannot be two elements in the hash table that are equal (the
comparison function returns 0 for them).
It is up to the user to handle collisions.
.PP
\fIhash_uninstall\fR removes an element from a table.
The argument is a pointer to a datum that identifies the element.
.PP
\fIhash_iter\fR goes through every element in the hash table
and calls the \fIdoit\fR function for each.
The first argument it provides to \fIdoit\fR is the element in question,
the second is whatever was given to \fIhash_iter\fR as \fIparam\fR.
If \fIdoit\fR returns -1 or 0 for any element in the hash table,
\fIhash_iter\fR immediately returns without going through the remaining
elements in the hash table.
Any other return value from \fIdoit\fR is ignored.
.SH RETURNS
\fIhash_create\fR returns a pointer to the new hash table, or NULL if
it fails.
.PP
\fIhash_install\fR returns a pointer to an element in the table
(either the installed one, or one that was already installed, if one
tries to install the same datum twice).
.PP
\fIhash_uninstall\fR returns 0 if it found the element in the array,
or -1 if it didn't.
.PP
\fIhash_lookup\fR return a pointer to the element it finds, or NULL if
it doesn't find anything beautiful.
.PP
\fIhash_iter\fR returns -1, 0, or 1.  If \fIhash_iter\fR receives a
return value of -1 or 0 for some element from \fIdoit\fR,
\fIhash_iter\fR immediately returns -1 or 0, respectively.
In all other cases \fIhash_iter\fR returns 1.
.SH "SEE ALSO"
publib(3), qsort(3), bsearch(3)
.SH AUTHOR
Lars Wirzenius (lars.wirzenius@helsinki.fi)