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 compared.

       Undefined results can occur if there is not enough room in the table to add a new item.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       hcreate(), tdelete()

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

COPYRIGHT

       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 .