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
- 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
Name of the comparison function which 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()
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 being compared.
Although declared as type pointer-to-character,
the value returned should be cast into type pointer-to-element.
EXAMPLES
This code fragment reads in ≤
TABSIZE
strings of length ≤
ELSIZE
and stores them in a table, eliminating duplicates.
#include <stdio.h>
#define TABSIZE 50
#define ELSIZE 120
char line[ELSIZE], tab[TABSIZE][ELSIZE], *lsearch( );
size_t nel = 0;
int strcmp( );
...
while (fgets(line, ELSIZE, stdin) != NULL &&
nel < TABSIZE)
(void) lsearch(line, (char *)tab, &nel,
ELSIZE, strcmp);
...
RETURN VALUE
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.
WARNINGS
Undefined results can occur
if there is not enough room in the table to add a new item.
STANDARDS CONFORMANCE
lsearch(): AES, SVID2, SVID3, XPG2, XPG3, XPG4
lfind(): AES, SVID2, SVID3, XPG2, XPG3, XPG4