lsearch, lfind - linear search and update
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 *));
The lsearch() function is a linear search routine general-
ized 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. 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 exam-
ple). It is called with two arguments that point to the ele-
ments 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 may be pointers to any type.
o The comparison function need not compare every byte,
so arbitrary data may be contained in the elements in
addition to the values being compared.
o The value returned should be cast into type pointer-
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
Undefined results can occur if there is not enough room in
the table to add a new item.
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, eliminat-
ing duplicates, and then will print each entry.
#define TABSIZE 50
#define ELSIZE 120
char line[ELSIZE]; /* buffer to hold input string */
char tab[TABSIZE][ELSIZE]; /* table of strings */
size_t nel = 0; /* number of entries in tab */
while (fgets(line, ELSIZE, stdin) != NULL &&
nel < TABSIZE)
(void) lsearch(line, tab, &nel, ELSIZE, mycmp);
for( i = 0; i < nel; i++ )
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | Safe |
bsearch(3C), hsearch(3C), string(3C), tsearch(3C), attri-
The Art of Computer Programming, Volume 3, Sorting and
Searching by Donald E. Knuth, published by Addison-Wesley
Publishing Company, 1973.
Man(1) output converted with