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LSEARCH(3P) POSIX Programmer's Manual LSEARCH(3P)
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.
lsearch, lfind — linear search and update
#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 *));
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.
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.
No errors are defined.
The following sections are informative.
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);
The comparison function need not compare every byte, so arbitrary
data may be contained in the elements in addition to the values being
compared.
Undefined results can occur if there is not enough room in the table
to add a new item.
None.
None.
hcreate(3p), tdelete(3p)
The Base Definitions volume of POSIX.1‐2008, search.h(0p)
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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 LSEARCH(3P)
Pages that refer to this page: search.h(0p), bsearch(3p), hcreate(3p), lfind(3p), tdelete(3p)