Tribblix: manual page: lsearch.3c

LSEARCH(3C) Standard C Library Functions LSEARCH(3C)

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 is a linear search routine generalized from
Knuth (6.1) Algorithm S. (see The Art of Computer Programming, Volume
3, Section 6.1, by Donald E. Knuth.). It returns a pointer to a table
indicating where a datum can be found. If the datum does not occur,
it is added at the end of the table. The key argument points to the
datum to be sought in the table. The base argument points to the
first element in the table. The nelp argument points to an integer
containing the current number of elements in the table. The integer
is incremented if the datum is added to the table. The width argument
is the size of an element in bytes. The compar argument is a pointer
to the comparison function that the user must supply (strcmp(3C) for
example). It is called with two arguments that point to the elements
being compared. The function must return zero if the elements are
equal and non-zero otherwise.

The lfind() function is the same as lsearch() except that if the
datum is not found, it is not added to the table. Instead, a null
pointer is returned.

It is important to note the following:

o The pointers to the key and the element at the base of the
table can be pointers to any type.

o The comparison function need not compare every byte, so
arbitrary data can be contained in the elements in
addition to the values being compared.

o The value returned should be cast into type pointer-to-
element.

RETURN VALUES

If the searched-for datum is found, both lsearch() and lfind()
return a pointer to it. Otherwise, lfind() returns NULL and lsearch()
returns a pointer to the newly added element.

USAGE

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

The lsearch() and lfind() functions safely allows concurrent access
by multiple threads to disjoint data, such as overlapping subtrees or
tables.

EXAMPLES

Example 1: A sample code using the lsearch() function.

This program will read in less than TABSIZE strings of length less
than ELSIZE and store them in a table, eliminating duplicates, and
then will print each entry.

#include <search.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#define TABSIZE 50
#define ELSIZE 120

main()
{
char line[ELSIZE]; /* buffer to hold input string */
char tab[TABSIZE][ELSIZE]; /* table of strings */
size_t nel = 0; /* number of entries in tab */
int i;

while (fgets(line, ELSIZE, stdin) != NULL &&
nel < TABSIZE)
(void) lsearch(line, tab, &nel, ELSIZE, mycmp);
for( i = 0; i < nel; i++ )
(void)fputs(tab[i], stdout);
return 0;
}

ATTRIBUTES