lsearch(3p) — Linux manual page


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

PROLOG         top

       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         top

       lsearch, lfind — linear search and update

SYNOPSIS         top

       #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         top

       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

       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         top

       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         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   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.

RATIONALE         top




SEE ALSO         top

       hcreate(3p), tdelete(3p)

       The Base Definitions volume of POSIX.1‐2017, search.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                       LSEARCH(3P)

Pages that refer to this page: search.h(0p)bsearch(3p)hcreate(3p)lfind(3p)tdelete(3p)