lsearch(3C)

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.

APPLICATION USAGE

lfind() and lsearch() are thread-safe and async-cancel-safe.

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( ); 
    unsigned 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