std::bsearch

#include <cstdlib>
#include <iostream>

int compare(const void *ap, const void *bp)
{
    const int *a = (int *) ap;
    const int *b = (int *) bp;
    return *a - *b;
}

int show_ptr(int *p) 
{
    if (p == NULL) {
        std::cout << "NULL\n";
    } else {
        std::cout << p1 << ' ' << *p1 << '\n';
    }
}

int main(int argc, char **argv)
{
    const int ARR_SIZE = 8;
    int arr[ARR_SIZE] = { 1, 2, 3, 4, 5, 6, 7, 8 };

    int key1 = 4;
    int *p1 = (int *) std::bsearch(&key1, arr, ARR_SIZE, sizeof(arr[0]), compare);

    int key2 = 9;
    int *p2 = (int *) std::bsearch(&key2, arr, ARR_SIZE, sizeof(arr[0]), compare);

    std::cout << "p1: ";
    show_ptr(p1);

    std::cout << "p2: ";
    show_ptr(p2);
}