Thread: Problem Using bsearch

> Am I even using bsearch correctly?
I would suggest that's a NO

Normally, I would do
struct person lookup;

and copy the appropriate information from the user into this structure.

This means you can use compare() as the search function and get rid of compare2() altogether. At the very least, you don't have to worry whether lookup is passed to compare() as the first or second parameter.

> strncpy(lookup,tok,3);
Here's another mistake - this doesn't mean that it has a \0 on the end to make it a proper string.

> I seem to be getting a segmentation fault from the printf statement
Have you printed the sorted array just to verify that the array is in fact sorted correctly.

Sounds about right to me

You shouldn't need to cast anything

Does this help?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct person
{
   char name[32];
   int  num;
};

int cmp_name(const void *a, const void *b)
{
   const struct person *x = a, *y = b;
   return strcmp(x->name, y->name);
}

int cmp_num(const void *a, const void *b)
{
   const struct person *x = a, *y = b;
   return (x->num > y->num) - (x->num < y->num);
}

void display(const char *label, const struct person *p, size_t size)
{
   puts(label);
   for ( ; size--; ++p )
   {
      printf("name = \"%s\", num = %d\n", p->name, p->num);
   }
   putchar('\n');
}

int main(void)
{
   struct person *found, key, in[] =
   {
      {"Fred", 7},
      {"Anne", 4},
      {"Paul", 3},
      {"Judy", 6},
      {"Jeff", 5},
      {"Jose", 1},
      {"Vlad", 2},
   };
   size_t count = sizeof in / sizeof *in; /* number of records */
   display("Unsorted:", in, count);
   /*
    * Search for a particular 'name'. Make sure the array is sorted by 'name'.
    */
   qsort(in, count, sizeof *in, cmp_name);
   display("Sorted by 'name':", in, count);

   strcpy(key.name, "Jeff");
   printf("Searching for 'name' = \"%s\"... ", key.name);
   found = bsearch(&key, in, count, sizeof *in, cmp_name);
   if ( found )
   {
      printf("'num' = %d\n\n", found->num);
   }
   else
   {
      puts("not found.\n");
   }
   /*
    * Search for a particular 'num'. Make sure the array is sorted by 'num'.
    */
   qsort(in, count, sizeof *in, cmp_num);
   display("Sorted by 'num':", in, count);

   key.num = 3;
   printf("Searching for 'num' = %d... ", key.num);
   found = bsearch(&key, in, count, sizeof *in, cmp_num);
   if ( found )
   {
      printf("'name' = \"%s\".\n\n", found->name);
   }
   else
   {
      puts("not found.\n");
   }
   return 0;
}

/* my output
Unsorted:
name = "Fred", num = 7
name = "Anne", num = 4
name = "Paul", num = 3
name = "Judy", num = 6
name = "Jeff", num = 5
name = "Jose", num = 1
name = "Vlad", num = 2

Sorted by 'name':
name = "Anne", num = 4
name = "Fred", num = 7
name = "Jeff", num = 5
name = "Jose", num = 1
name = "Judy", num = 6
name = "Paul", num = 3
name = "Vlad", num = 2

Searching for 'name' = "Jeff"... 'num' = 5

Sorted by 'num':
name = "Jose", num = 1
name = "Vlad", num = 2
name = "Paul", num = 3
name = "Anne", num = 4
name = "Jeff", num = 5
name = "Judy", num = 6
name = "Fred", num = 7

Searching for 'num' = 3... 'name' = "Paul".
*/