Built-In Searching

• The following routines are declared in stdlib.h:

  void *bsearch(const void *key, const void *base, unsigned int tsize,
                unsigned int esize, int (*compare)(const void *, const void *));
  void qsort(void *base, unsigned int tsize, unsigned int esize,
          int (*compare)(const void *, const void *));
  

• bsearch performs a binary search into the sorted array base. It looks for what key is pointing to, and returns a pointer to it if it is found and NULL otherwise. tsize should be the size of the array, and esize the size of each element in the array. compare should be a comparison function taking two pointers to elements and returning a boolean in such a way that i > j implies compare( &(a[i]), &(a[j]) );.

  Here is an example:

  int icomp(void *a, void *b)
  {
    return( *( (int *) a) > *( (int *) b) );
  }
  
  int main()
  {
    int i, a[100];
    for ( i = 0; i < 100; i++ )
       a[i] = i * i + i;
    i = 37;
  
    printf( "%d", bsearch(&i, a, 100, sizeof(int), icomp );
  }
  

• qsort preforms a quick sort of the array base. tsize, esize, and compare are as in bsearch. Here is an example:

    int i, a[100];
    for ( i = 0; i < 100; i++ )
       a[i] = rand();
  
    qsort( a, 100, sizeof(int), icomp );
  

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