bionic (3) lsearch.3posix.gz

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.1‐2008, <search.h>

COPYRIGHT

       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 .