What is bsearch_s() in C?
bsearch_s is a built-in function defined in the <stdlib.h> header. It is available for use from the C11 version of C.
To use the function, we must define __STDC_LIB_EXT1__ and set __STDC_WANT_LIB_EXT1__ to 1.
Below is the function prototype:
void* bsearch_s (const void *key, const void *arr, rsize_t count, rsize_t size, int (*comp)(const void *, const void *, void *), void *context);
Parameters
Let’s take a deeper look into the input parameters of the function.
- key: Pointer to the element being found.
- arr: Pointer to the array being searched.
- count: Total number of elements in the array.
- size: Size, in bytes, of each element in the array.
- comp: Pointer to the comparison function.
- context: Additional information to serve as context for comp.
Return
The
bsearch_sfunction returns a pointer to the key element.
If the key element is not found or dealt with a runtime error, a null pointer is returned.
The comparison function
Below the prototype for the comp function:
int cmp(const void *key, const void *element, void* context);
The first argument is the key that we find, while the second argument may be any element from the array.
The comp function returns:
-
-1if the key is less than the element -
0if the key is equal to the element -
1if the key is greater than the element
Code
#define __STDC_WANT_LIB_EXT1__ 1
#include <stdlib.h>
#include <stdio.h>
int comp(void const *lhs, void const *rhs, void* context)
{
const int* l = (const int*) lhs;
const int* r = (const int*)rhs;
if (*l < *r) return -1;
else if (*l > *r) return 1;
else return 0;
}
int main()
{
int arr[] = {0, 2, 4, 6, 8, 10};
int key = 4;
int* result = bsearch_s(&key, arr, sizeof(arr) / sizeof(arr[0]), sizeof(arr[0]), comp, NULL);
if(result)
printf("\n%d found\n", *result);
else
printf( "\nNot found!\n" );
}
Here we’re dealing with a simple integer array; hence, there is no need for context and we can pass NULL in its place.
Note that the array we are searching is sorted. This is a pre-requisite for
binary search.
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