lsearch(3C) manual page
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lsearch, lfind - linear search and update
#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 *));
Safe
lsearch() 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
into a table indicating where a datum may be found. If the datum does not
occur, it is added at the end of the table. key points to the datum to be
sought in the table. base points to the first element in the table. nelp
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. width
is the size of an element in bytes. compar is a pointer to the comparison
function that the user must supply (strcmp, 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.
lfind() 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.
Note that:
- the
pointers to the key and the element at the base of the table may be pointers
to any type.
- The comparison function need not compare every byte, so arbitrary
data may be contained in the elements in addition to the values being compared.
- The value returned should be cast into type pointer-to-element.
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;
}
bsearch(3C)
, hsearch(3C)
, string(3C)
, tsearch(3C)
The Art of Computer Programming, Volume 3, Sorting and Searching by Donald
E. Knuth, published by Addison-Wesley Publishing Company, 1973.
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.
Undefined results can occur if there is not
enough room in the table to add a new item.
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