searching

代码说明：

  /* binarysearch() - A binary search implementation which takes the same * arguments as the C library function bsearch() provided by stdlib.h. It * searches the sorted array at address base, which has nmemb elements, each of * which is size bytes long. compar is a pointer to a comparison function. * The function compares two array elements, and returns a negative, zero, or * positive integer depending on whether the first array element is less than, * equal to, or greater than the second. */