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lsearch, lfind – linear search and append

LIBRARY SYNOPSIS DESCRIPTION RETURN VALUES EXAMPLES SEE ALSO STANDARDS HISTORY

Standard C Library (libc, -lc)

#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() and lfind() functions walk linearly through an array and compare each element with the one to be sought using a supplied comparison function.

The key argument points to an element that matches the one that is searched. The array's address in memory is denoted by the base argument. The width of one element (i.e., the size as returned by sizeof()) is passed as the width argument. The number of valid elements contained in the array (not the number of elements the array has space reserved for) is given in the integer pointed to by nelp. The compar argument points to a function which compares its two arguments and returns zero if they are matching, and non-zero otherwise.

If no matching element was found in the array, lsearch() copies key into the position after the last element and increments the integer pointed to by nelp.

The lsearch() and lfind() functions return a pointer to the first element found. If no element was found, lsearch() returns a pointer to the newly added element, whereas lfind() returns NULL. Both functions return NULL if an error occurs.

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

static int
element_compare(const void *p1, const void *p2)
{
        int left = *(const int *)p1;
        int right = *(const int *)p2;

        return (left - right);
}

int
main(int argc, char **argv)
{
        const int array[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        size_t element_size = sizeof(array[0]);
        size_t array_size = sizeof(array) / element_size;
        int key;
        void *element;

        printf("Enter a number: ");
        if (scanf("%d", &key) != 1) {
                printf("Bad input\n");
                return (EXIT_FAILURE);
        }

        element = lfind(&key, array, &array_size, element_size,
            element_compare);

        if (element != NULL)
                printf("Element found: %d\n", *(int *)element);
        else
                printf("Element not found\n");

        return (EXIT_SUCCESS);
}

The lsearch() and lfind() functions conform to IEEE Std 1003.1-2001 ("POSIX.1").

The lsearch() and lfind() functions appeared in BSD 4.2 . In FreeBSD 5.0, they reappeared conforming to IEEE Std 1003.1-2001 ("POSIX.1").