diff options
Diffstat (limited to 'man3/hsearch.3')
| -rw-r--r-- | man3/hsearch.3 | 355 |
1 files changed, 0 insertions, 355 deletions
diff --git a/man3/hsearch.3 b/man3/hsearch.3 deleted file mode 100644 index 93e6794..0000000 --- a/man3/hsearch.3 +++ /dev/null @@ -1,355 +0,0 @@ -'\" t -.\" Copyright 1993 Ulrich Drepper (drepper@karlsruhe.gmd.de) -.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk -.\" <mtk.manpages@gmail.com> -.\" -.\" SPDX-License-Identifier: GPL-2.0-or-later -.\" -.\" References consulted: -.\" SunOS 4.1.1 man pages -.\" Modified Sat Sep 30 21:52:01 1995 by Jim Van Zandt <jrv@vanzandt.mv.com> -.\" Remarks from dhw@gamgee.acad.emich.edu Fri Jun 19 06:46:31 1998 -.\" Modified 2001-12-26, 2003-11-28, 2004-05-20, aeb -.\" 2008-09-02, mtk: various additions and rewrites -.\" 2008-09-03, mtk, restructured somewhat, in part after suggestions from -.\" Timothy S. Nelson <wayland@wayland.id.au> -.\" -.TH hsearch 3 2023-10-31 "Linux man-pages 6.7" -.SH NAME -hcreate, hdestroy, hsearch, hcreate_r, hdestroy_r, -hsearch_r \- hash table management -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.B #include <search.h> -.P -.BI "int hcreate(size_t " nel ); -.B "void hdestroy(void);" -.P -.BI "ENTRY *hsearch(ENTRY " item ", ACTION " action ); -.P -.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" -.B #include <search.h> -.P -.BI "int hcreate_r(size_t " nel ", struct hsearch_data *" htab ); -.BI "void hdestroy_r(struct hsearch_data *" htab ); -.P -.BI "int hsearch_r(ENTRY " item ", ACTION " action ", ENTRY **" retval , -.BI " struct hsearch_data *" htab ); -.fi -.SH DESCRIPTION -The three functions -.BR hcreate (), -.BR hsearch (), -and -.BR hdestroy () -allow the caller to create and manage a hash search table -containing entries consisting of a key (a string) and associated data. -Using these functions, only one hash table can be used at a time. -.P -The three functions -.BR hcreate_r (), -.BR hsearch_r (), -.BR hdestroy_r () -are reentrant versions that allow a program to use -more than one hash search table at the same time. -The last argument, -.IR htab , -points to a structure that describes the table -on which the function is to operate. -The programmer should treat this structure as opaque -(i.e., do not attempt to directly access or modify -the fields in this structure). -.P -First a hash table must be created using -.BR hcreate (). -The argument \fInel\fP specifies the maximum number of entries -in the table. -(This maximum cannot be changed later, so choose it wisely.) -The implementation may adjust this value upward to improve the -performance of the resulting hash table. -.\" e.g., in glibc it is raised to the next higher prime number -.P -The -.BR hcreate_r () -function performs the same task as -.BR hcreate (), -but for the table described by the structure -.IR *htab . -The structure pointed to by -.I htab -must be zeroed before the first call to -.BR hcreate_r (). -.P -The function -.BR hdestroy () -frees the memory occupied by the hash table that was created by -.BR hcreate (). -After calling -.BR hdestroy (), -a new hash table can be created using -.BR hcreate (). -The -.BR hdestroy_r () -function performs the analogous task for a hash table described by -.IR *htab , -which was previously created using -.BR hcreate_r (). -.P -The -.BR hsearch () -function searches the hash table for an -item with the same key as \fIitem\fP (where "the same" is determined using -.BR strcmp (3)), -and if successful returns a pointer to it. -.P -The argument \fIitem\fP is of type \fIENTRY\fP, which is defined in -\fI<search.h>\fP as follows: -.P -.in +4n -.EX -typedef struct entry { - char *key; - void *data; -} ENTRY; -.EE -.in -.P -The field \fIkey\fP points to a null-terminated string which is the -search key. -The field \fIdata\fP points to data that is associated with that key. -.P -The argument \fIaction\fP determines what -.BR hsearch () -does after an unsuccessful search. -This argument must either have the value -.BR ENTER , -meaning insert a copy of -.I item -(and return a pointer to the new hash table entry as the function result), -or the value -.BR FIND , -meaning that NULL should be returned. -(If -.I action -is -.BR FIND , -then -.I data -is ignored.) -.P -The -.BR hsearch_r () -function is like -.BR hsearch () -but operates on the hash table described by -.IR *htab . -The -.BR hsearch_r () -function differs from -.BR hsearch () -in that a pointer to the found item is returned in -.IR *retval , -rather than as the function result. -.SH RETURN VALUE -.BR hcreate () -and -.BR hcreate_r () -return nonzero on success. -They return 0 on error, with -.I errno -set to indicate the error. -.P -On success, -.BR hsearch () -returns a pointer to an entry in the hash table. -.BR hsearch () -returns NULL on error, that is, -if \fIaction\fP is \fBENTER\fP and -the hash table is full, or \fIaction\fP is \fBFIND\fP and \fIitem\fP -cannot be found in the hash table. -.BR hsearch_r () -returns nonzero on success, and 0 on error. -In the event of an error, these two functions set -.I errno -to indicate the error. -.SH ERRORS -.BR hcreate_r () -and -.BR hdestroy_r () -can fail for the following reasons: -.TP -.B EINVAL -.I htab -is NULL. -.P -.BR hsearch () -and -.BR hsearch_r () -can fail for the following reasons: -.TP -.B ENOMEM -.I action -was -.BR ENTER , -.I key -was not found in the table, -and there was no room in the table to add a new entry. -.TP -.B ESRCH -.I action -was -.BR FIND , -and -.I key -was not found in the table. -.P -POSIX.1 specifies only the -.\" PROX.1-2001, POSIX.1-2008 -.B ENOMEM -error. -.SH ATTRIBUTES -For an explanation of the terms used in this section, see -.BR attributes (7). -.TS -allbox; -lbx lb lb -l l l. -Interface Attribute Value -T{ -.na -.nh -.BR hcreate (), -.BR hsearch (), -.BR hdestroy () -T} Thread safety MT-Unsafe race:hsearch -T{ -.na -.nh -.BR hcreate_r (), -.BR hsearch_r (), -.BR hdestroy_r () -T} Thread safety MT-Safe race:htab -.TE -.SH STANDARDS -.TP -.BR hcreate () -.TQ -.BR hsearch () -.TQ -.BR hdestroy () -POSIX.1-2008. -.TP -.BR hcreate_r () -.TQ -.BR hsearch_r () -.TQ -.BR hdestroy_r () -GNU. -.SH HISTORY -.TP -.BR hcreate () -.TQ -.BR hsearch () -.TQ -.BR hdestroy () -SVr4, POSIX.1-2001. -.TP -.BR hcreate_r () -.TQ -.BR hsearch_r () -.TQ -.BR hdestroy_r () -GNU. -.SH NOTES -Hash table implementations are usually more efficient when the -table contains enough free space to minimize collisions. -Typically, this means that -.I nel -should be at least 25% larger than the maximum number of elements -that the caller expects to store in the table. -.P -The -.BR hdestroy () -and -.BR hdestroy_r () -functions do not free the buffers pointed to by the -.I key -and -.I data -elements of the hash table entries. -(It can't do this because it doesn't know -whether these buffers were allocated dynamically.) -If these buffers need to be freed (perhaps because the program -is repeatedly creating and destroying hash tables, -rather than creating a single table whose lifetime -matches that of the program), -then the program must maintain bookkeeping data structures that -allow it to free them. -.SH BUGS -SVr4 and POSIX.1-2001 specify that \fIaction\fP -is significant only for unsuccessful searches, so that an \fBENTER\fP -should not do anything for a successful search. -In libc and glibc (before glibc 2.3), the -implementation violates the specification, -updating the \fIdata\fP for the given \fIkey\fP in this case. -.P -Individual hash table entries can be added, but not deleted. -.SH EXAMPLES -The following program inserts 24 items into a hash table, then prints -some of them. -.P -.\" SRC BEGIN (hsearch.c) -.EX -#include <search.h> -#include <stdio.h> -#include <stdlib.h> -\& -static char *data[] = { "alpha", "bravo", "charlie", "delta", - "echo", "foxtrot", "golf", "hotel", "india", "juliet", - "kilo", "lima", "mike", "november", "oscar", "papa", - "quebec", "romeo", "sierra", "tango", "uniform", - "victor", "whisky", "x\-ray", "yankee", "zulu" -}; -\& -int -main(void) -{ - ENTRY e; - ENTRY *ep; -\& - hcreate(30); -\& - for (size_t i = 0; i < 24; i++) { - e.key = data[i]; - /* data is just an integer, instead of a - pointer to something */ - e.data = (void *) i; - ep = hsearch(e, ENTER); - /* there should be no failures */ - if (ep == NULL) { - fprintf(stderr, "entry failed\en"); - exit(EXIT_FAILURE); - } - } -\& - for (size_t i = 22; i < 26; i++) { - /* print two entries from the table, and - show that two are not in the table */ - e.key = data[i]; - ep = hsearch(e, FIND); - printf("%9.9s \-> %9.9s:%d\en", e.key, - ep ? ep\->key : "NULL", ep ? (int)(ep\->data) : 0); - } - hdestroy(); - exit(EXIT_SUCCESS); -} -.EE -.\" SRC END -.SH SEE ALSO -.BR bsearch (3), -.BR lsearch (3), -.BR malloc (3), -.BR tsearch (3) |