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 ele‐
ment in the table. The nelp argument points to an integer containing
the current number of elements in the table. The integer is incre‐
mented 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 com‐
pared. 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:
· The pointers to the key and the element at the base of the table
can be pointers to any type.
· The comparison function need not compare every byte, so arbitrary
data can be contained in the elements in addition to the values
being compared.
· 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
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSObsearch(3C), hsearch(3C), string(3C), tsearch(3C), attributes(5), stan‐
dards(5)
The Art of Computer Programming, Volume 3, Sorting and Searching by
Donald E. Knuth, published by Addison-Wesley Publishing Company, 1973.
SunOS 5.10 6 Dec 2004 lsearch(3C)
