bsearch(3) [linux man page]

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 according 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.

CONFORMING TO

       SVr4, 4.3BSD, POSIX.1-2001, C89, C99.

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(struct mi))

       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
", argv[i]);
	       else
		   printf("%s: month #%d
", res->name, res->nr);
	   }
	   exit(EXIT_SUCCESS);
       }

SEE ALSO

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

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

								    2003-11-01								BSEARCH(3)

Check Out this Related Man Page

QSORT(3)						     Linux Programmer's Manual							  QSORT(3)

NAME

       qsort - sorts an array

SYNOPSIS

       #include <stdlib.h>

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

DESCRIPTION

       The qsort() function sorts an array with nmemb elements of size size.  The base argument points to the start of the array.

       The  contents  of the array are sorted in ascending order according to a comparison function pointed to by compar, which is called with two
       arguments that point to the objects being compared.

       The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be  respec-
       tively less than, equal to, or greater than the second.	If two members compare as equal, their order in the sorted array is undefined.

RETURN VALUE

       The qsort() function returns no value.

CONFORMING TO

       SVr4, 4.3BSD, C89, C99.

NOTES

       Library	routines  suitable  for  use as the compar argument include alphasort(3) and versionsort(3).  To compare C strings, the comparison
       function can call strcmp(3), as shown in the example below.

EXAMPLE

       For one example of use, see the example under bsearch(3).

       Another example is the following program, which sorts the strings given in its command-line arguments:

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

       static int
       cmpstringp(const void *p1, const void *p2)
       {
	   /* The actual arguments to this function are "pointers to
	      pointers to char", but strcmp(3) arguments are "pointers
	      to char", hence the following cast plus dereference */

	   return strcmp(* (char * const *) p1, * (char * const *) p2);
       }

       int
       main(int argc, char *argv[])
       {
	   int j;

	   if (argc < 2) {
	    fprintf(stderr, "Usage: %s <string>...
", argv[0]);
	    exit(EXIT_FAILURE);
	   }

	   qsort(&argv[1], argc - 1, sizeof(argv[1]), cmpstringp);

	   for (j = 1; j < argc; j++)
	       puts(argv[j]);
	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       sort(1), alphasort(3), strcmp(3), versionsort(3)

COLOPHON

       This page is part of release 3.27 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

								    2009-09-15								  QSORT(3)

Linux and UNIX Man Pages

bsearch(3) [linux man page]

Check Out this Related Man Page