bsearch

BSEARCH(3)		  Linux Programmer’s Manual		   BSEARCH(3)



NAME
       bsearch - binary search of a sorted array

SYNOPSIS
       #include <stdlib.h>

       void *bsearch(const void *key, const void *base, size_t nmemb,
	      size_t size, int (*compar)(const void *, const void *));

DESCRIPTION
       The bsearch() function searches an array of nmemb objects, the initial
       member of which is pointed to by base, for a member that	 matches  the
       object  pointed	to  by	key.  The size of each member of the array is
       specified by size.

       The contents of the array should be in ascending sorted order  accord-
       ing  to the comparison function referenced by compar.  The compar rou-
       tine is expected to have two arguments which point to the  key  object
       and  to	an  array member, in that order, and should return an integer
       less than, equal to, or greater than zero if the key object is  found,
       respectively,  to be less than, to match, or be greater than the array
       member.

RETURN VALUE
       The bsearch() function returns a pointer to a matching member  of  the
       array,  or  NULL if no match is found.  If there are multiple elements
       that match the key, the element returned is unspecified.

EXAMPLE
       The example below first sorts an array of structures  using  qsort(3),
       then retrieves desired elements using bsearch().

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

       struct mi {
	    int nr;
	    char *name;
       } months[] = {
	    { 1, "jan" }, { 2, "feb" }, { 3, "mar" }, { 4, "apr" },
	    { 5, "may" }, { 6, "jun" }, { 7, "jul" }, { 8, "aug" },
	    { 9, "sep" }, {10, "oct" }, {11, "nov" }, {12, "dec" }
       };

       #define nr_of_months (sizeof(months)/sizeof(months[0]))

       static int compmi(const void *m1, const void *m2) {
	    struct mi *mi1 = (struct mi *) m1;
	    struct mi *mi2 = (struct mi *) m2;
	    return strcmp(mi1->name, mi2->name);
       }

       int main(int argc, char **argv) {
	    int i;

	    qsort(months, nr_of_months, sizeof(struct mi), compmi);
	    for (i = 1; i < argc; i++) {
		 struct mi key, *res;
		 key.name = argv[i];
		 res = bsearch(&key, months, nr_of_months,
			    sizeof(struct mi), compmi);
		 if (res == NULL)
		      printf("’%s’: unknown month\n", argv[i]);
		 else
		      printf("%s: month #%d\n", res->name, res->nr);
	    }
	    return 0;
       }

CONFORMING TO
       SVID 3, BSD 4.3, ISO 9899 (C99)

SEE ALSO
       hsearch(3), lsearch(3), tsearch(3), qsort(3)



				  2003-11-01			   BSEARCH(3)