LSEARCH(3)                 POSIX Programmer's Manual                LSEARCH(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 aa 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 aa Matching Entry
       The following example finds any line that reads ""TThhiissisaatest."..


           #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 .



IEEE/The Open Group                  2017                           LSEARCH(3)
