lsearch(3C)

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 data may be found. If the data does not occur, it is added at the end of the table. key points to the data 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 data 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 data is not found, it is not added to the table. Instead, a null pointer is returned.

Return values

If the searched-for data 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.

Usage

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;
   }

References

bsearch(3C), hsearch(3C), string(3C), tsearch(3C)

Notices

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.

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