lsearch(3)
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lsearch, lfind Subroutine
linear search and update
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SYNTAX
#include <stdio.h>
#include <search.h>
char *lsearch ((char *)key, (char *)base, nelp, sizeof(*key),
compar)
unsigned *nelp;
int (*compar)( );
char *lfind ((char *)key, (char *)base, nelp, sizeof(*key),
compar)
unsigned *nelp;
int (*compar)( );
DESCRIPTION
Lsearch is a linear search routine generalized from Knuth (6.1)
Algorithm S. 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.
Compar is the name of the comparison function, which you 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.
NOTES
The pointers to the key and the element at the base of the table
should be of type pointer-to-element, and cast to type pointer-
to-character.
The comparison function need not compare every byte, so arbitrary
data may be contained in the elements in addition to the values
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lsearch(3)
being compared.
Although declared as type pointer-to-character, the value
returned should be cast into type pointer-to-element.
EXAMPLE
This fragment will read in < TABSIZE strings of length < ELSIZE
and store them in a table, eliminating duplicates.
#include <stdio.h>
#include <search.h>
#define TABSIZE 50
#define ELSIZE 120
char line[ELSIZE], tab[TABSIZE][ELSIZE], *lsearch( );
unsigned nel = 0;
int strcmp( );
. . .
while (fgets(line, ELSIZE, stdin) != NULL &&
nel < TABSIZE)
(void) lsearch(line, (char *)tab, &nel,
ELSIZE, strcmp);
. . .
SEE ALSO
bsearch(3C), hsearch(3C), tsearch(3C).
DIAGNOSTICS
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.
BUGS
Undefined results can occur if there is not enough room in the
table to add a new item.
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