The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


lsearch, lfind - linear search and update


#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 *));


The lsearch() function is a linear search routine. 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 width argument is the size of an element in bytes. The nelp argument points to an integer containing the current number of elements in the table. The integer to which nelp points is incremented if the entry is added to the table. The compar argument points to a comparison function which the user must supply (.Fn strcmp , for example). It is called with two arguments that point to the elements being compared. The function must return 0 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.


If the searched for entry is found, both lsearch() and lfind() return a pointer to it. Otherwise, lfind() returns a null pointer and lsearch() returns a pointer to the newly added element.

Both functions return a null pointer in case of error.


No errors are defined.


This fragment will read in less than or equal to TABSIZE strings of length less than or equal to ELSIZE and store them in a table, eliminating duplicates.

#include <stdio.h>
#include <string.h>
#include <search.h>

#define TABSIZE 50
#define ELSIZE 120

    char line[ELSIZE], tab[TABSIZE][ELSIZE];
    size_t nel = 0;
    while (fgets(line, ELSIZE, stdin) != NULL && nel < TABSIZE)
        (void) lsearch(line, tab, &nel,
            ELSIZE, (int (*)(const void *, const void *)) strcmp);


The comparison function need not compare every byte, so arbitrary data may be contained in the elements in addition to the values being compared.

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




bsearch(), hsearch(), tsearch(), <search.h>.


Derived from Issue 1 of the SVID.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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