lsearch(S)

lsearch, lfind -- linear search and update

Syntax

cc . . . -lc

#include <search.h>

void *lsearch (const void *key, void *base, size_t *nelp, size_twidth,
	       int (*compar) (const void *));

void *lfind (const void *key, const void *base, size_t, *nelp,
	     size_twidth, int (*compar) (const void *, const void * ));

Description

lsearch- performs linear search of table

lfind- searches for object and adds to table

The lsearch function is a linear search routine generalized from Knuth (6.1) Algorithm S. It returns a pointer into a table indicating where an entry may be found. If the entry does not occur, it is added at the end of the table. The key argument points to the entry 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 width argument is the size of an element in bytes. The integer is incremented if the entry is added to the table. The compar argument is the 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.

The lfind function is the same as lsearch except that if the entry is not found, it is not added to the table. Instead, a NULL pointer is returned.

Example

This fragment reads in less than TABSIZE strings of length less than ELSIZE and stores 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( );
           size_t nel = 0;
           int strcmp( );
           . . .
           while (fgets(line, ELSIZE, stdin) != NULL &&
              nel < TABSIZE)
                   (void) lsearch((void *)line, (tab *)tab, &nel,
                             ELSIZE, strcmp);
           . . .

Diagnostics

If the searched-for entry 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.

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.

Undefined results can occur if there is not enough room in the table to add a new item.

Standards conformance

lfind and lsearch are conformant with:

X/Open Portability Guide, Issue 3, 1989 .