PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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 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         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);

APPLICATION USAGE         top

       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

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       hcreate(3p), tdelete(3p)

       The Base Definitions volume of POSIX.1‐2008, search.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                         LSEARCH(3P)