This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       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(3POSIX)

       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.

       No errors are defined.

       Thefollowingsectionsareinformative.

StoringStringsinaTable
       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);
               ...

   FindingaMatchingEntry
       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);

       None.

       lsearch, lfind — linear search and update

       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.

       None.

       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.

hcreate(), tdelete()

       The Base Definitions volume of POSIX.1‐2017, <search.h>

       #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 *));