What is the bsearch() : C

[UseME]

I has just started to learn the C programming language. I don't know anything about the C language but From when I started to learn I noticed that the C language is the basic of all programming languages. I heard about the library functions but I don't what are they and what they can do. So, I want know about the bsearch() function of the C language. I also want to know what is the purpose of the bsearch() function and how can I use the bsearch() function in the Coding.

[Katty]

According to my knowledge bsearch() function performs a binary search through the elements of a table. This bsearch() function can uses your compar() function to compare an elements in the table.You have to noticed that the compar() function you use could not do a byte-by-byte comparison between the table elements and the key. The following is the syntax of the bsearch() function :
#include <stdlib.h>
pt = bsearch( ky, tbl, tbsiz, kysz, cmpr);

[kelfro]

The bsearch() function can performs a binary search of a num elements of sorted array that matches the object pointed to by the key for an item. Each an array element is width bytes in size. The compar is the comparison function pointed can be called with two an arguments that can points to an array elements. This compar function must return an integer equal to, less than or greater than zero if the key object is equal to, less than or greater than the array element respectively.

[Zecho]

Example of bsearch() function :
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static const char *kywrds[] = {"auto", "break", "case", "char", "while"};
#define NUM_KW sizeof(kywrds) / sizeof(char *)
int kw_compare( const void *p3, const void *p4 )
{
const char *p3c = (const char *) p3;
const char **p4c = (const char **) p4;
return( strcmp( p3c, *p4c ) );
}
int kywrd_lookup( const char *nm )
{
const char **ky;
ky = (char const **) bsearch( nm, kywrds,
NUM_KW, sizeof( char * ), kw_compare );
if( ky == NULL ) return( -1 );
return ky - kywrds;
}
void main()
{
printf( "%d\n", kywrd_lookup( "case" ) );
printf( "%d\n", kywrd_lookup( "crigger" ) );
printf( "%d\n", kywrd_lookup( "auto" ) );
}

Output of the above program is as follows :
2
-1
0

[absolute55]

One more example on bsearch() function :
#include "config.h"
#include "ansidecl.h"
#include <sys/types.h>
#include <stdio.h>
void *
bsearch(key, base0, nmemb, size, compar)
register void *key;
void *base0;
size_t nmemb;
register size_t size;
register int (*compar)();
{
register char *base = base0;
register int lim, cmp;
register void *p;
for (lim = nmemb; lim != 0; lim >>= 1)
{
p = base + (lim >> 1) * size;
cmp = (*compar)(key, p);
if (cmp == 0)
return (p);
if (cmp > 0)
{
base = (char *)p + size;
lim--;
}
}
return (NULL);
}