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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)

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