LSEARCH(3P) POSIX Programmer's Manual LSEARCH(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
lsearch, lfind — linear search and update
SYNOPSIS
#include <search.h>
void *lsearch(const void *key, void *base, size_t *nelp, size_t width,
int (*compar)(const void *, const void *));
void *lfind(const void *key, const void *base, size_t *nelp,
size_t width, int (*compar)(const void *, const void *));
DESCRIPTION
The lsearch() function shall linearly search the table and return a
pointer into the table for the matching entry. If the entry does not
occur, it shall be added at the end of the table. The key argument
points to the entry to be sought in the table. The base argument points
to the first element in the table. The width argument is the size of an
element in bytes. The nelp argument points to an integer containing the
current number of elements in the table. The integer to which nelp
points shall be incremented if the entry is added to the table. The
compar argument points to a comparison function which the application
shall supply (for example, strcmp()). It is called with two arguments
that point to the elements being compared. The application shall ensure
that the function returns 0 if the elements are equal, and non-zero
otherwise.
The lfind() function shall be equivalent to lsearch(), except that if
the entry is not found, it is not added to the table. Instead, a null
pointer is returned.
RETURN VALUE
If the searched for entry is found, both lsearch() and lfind() shall
return a pointer to it. Otherwise, lfind() shall return a null pointer
and lsearch() shall return a pointer to the newly added element.
Both functions shall return a null pointer in case of error.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
Storing Strings in a Table
This fragment reads in less than or equal to TABSIZE strings of length
less than or equal to ELSIZE and stores them in a table, eliminating
duplicates.
#include <stdio.h>
#include <string.h>
#include <search.h>
#define TABSIZE 50
#define ELSIZE 120
...
char line[ELSIZE], tab[TABSIZE][ELSIZE];
size_t nel = 0;
...
while (fgets(line, ELSIZE, stdin) != NULL && nel < TABSIZE)
(void) lsearch(line, tab, &nel,
ELSIZE, (int (*)(const void *, const void *)) strcmp);
...
Finding a Matching Entry
The following example finds any line that reads "Thisisatest.".
#include <search.h>
#include <string.h>
...
char line[ELSIZE], tab[TABSIZE][ELSIZE];
size_t nel = 0;
char *findline;
void *entry;
findline = "This is a test.\n";
entry = lfind(findline, tab, &nel, ELSIZE, (
int (*)(const void *, const void *)) strcmp);
APPLICATION USAGE
The comparison function need not compare every byte, so arbitrary data
may be contained in the elements in addition to the values being com‐
pared.
Undefined results can occur if there is not enough room in the table to
add a new item.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOhcreate(), tdelete()
The Base Definitions volume of POSIX.1‐2008, <search.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 LSEARCH(3P)
