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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017, search.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. 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.opengroup.org/unix/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 2017 LSEARCH(3P)
Pages that refer to this page: search.h(0p), bsearch(3p), hcreate(3p), lfind(3p), tdelete(3p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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