binary search (bsearch) with 2 keys

deSertfiSh (6)
Hi Folks,

i´m focusing the following problem:

I want to select from the persons table the entry which matches 2 keys: FirstName & Age. However, the below code doesn´t do, it neglects the name and just regards the age as a single key. Any help would be gratful!

cheers
deSertfiSh

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct Person
{
  char * FirstName;
  char * FamilyName;
  int    Age;
};
 
int compareAge( void const * lhs, void const * rhs )
{
  struct Person * left  = ((struct Person *) lhs);
  struct Person * right = ((struct Person *) rhs);
 
  if(strcmp(left->FirstName , right->FirstName )) 
  {
    if( left->Age < right->Age ) return -1;
    if( left->Age > right->Age ) return 1;
  }
 
  return 0;
}
 
int main ( void )
{
  struct Person figures[] = { { "Max",  "Mustermann", 40 }
                            , { "Erika", "Mustermann", 38 }
                            , { "Jane", "Doe", 32 }
                            , { "Anna", "Gabler", 38 }
                            , { "John", "Doe", 34 }
                            , { "Anna", "Mustermann", 51 }
                            , { "Ann",  "MissX", 52 }
                            , { "Anne", "Mustermann", 53 }
                            , { "Anna", "Mustermann", 54 }
                            , { "Anna", "Mustermann", 55 }
                            , NULL };
 
  int const elements = 10;
  int const ageKey   = 52;
  char* const nameKey   = "Anni";
 
  int i = 0;
  
  qsort( figures, elements, sizeof( struct Person ), compareAge );
 
  struct Person key;
  key.Age = ageKey;
  key.FirstName = nameKey;
 
  struct Person* result = (Person*) bsearch( &key, figures, elements, sizeof( struct Person ), compareAge );
 
  if( result )
    printf( "gefunden: %s, %s (%d)\n", result->FamilyName, result->FirstName, result->Age );
  else
    printf( "nichts gefunden\n" );
 
  return EXIT_SUCCESS;
}


result is:

gefunden: MissX, Ann (52)
kooth (746)
Is your strcmp() supposed to see if these strings are equal? If so, you have it backwards. Strings are equal when strcmp() returns 0.
deSertfiSh (6)
ok, you are right, I modified to this:
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  if( strcmp(left->FirstName , right->FirstName ) == 0 )
  {
     if( left->Age == right->Age ) return 1;
  }
 
  return 0;


but anyway it doesn´t work :-(

deSertfiSh
kooth (746)
Don't you need to see if left-Age == right->Age?
vlad from moscow (6539)
Should you get the following?

Ann 52
Anna 38
Anna 51
Anna 54
Anna 55
Anne 53
Erika 38
Jane 32
John 34
Max 40
deSertfiSh (6)
no, I expect to be able to select 1 entry which matches

int const ageKey = 54;
char* const nameKey = "Anna"

So, i expect the result to be (f.ex.):

{ "Anna", "Mustermann", 54 }


deSertfiSh
vlad from moscow (6539)
Do not be hurry. I see that in the very beginning of your program the array is sorted. So I am asking should the array be sorted as I have shown? Have you the same sorted array before searching?
Last edited on
vlad from moscow (6539)
In any case try the following function

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int compareAge( void const * lhs, void const * rhs )
{
   struct Person * left  = ( struct Person * ) lhs;
   struct Person * right = ( struct Person * ) rhs;
 
   int result = strcmp( left->FirstName, right->FirstName );

   if ( result ) return ( result );
   else return ( left->Age - right->Age );
}
Last edited on
deSertfiSh (6)
Hey Vlad!

spasibo bolschoi, your suggestion really worked! Thx and greetings to Moscow!

deSertfiSh
vlad from moscow (6539)
Do you speak Russian?!
Last edited on
deSertfiSh (6)
net
kooth (746)
I meant that you should have all three comparisons in your compareAge() function:

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int compareAge( void const * lhs, void const * rhs )
    {
    struct Person * left  = ((struct Person *) lhs);
    struct Person * right = ((struct Person *) rhs);
 
    int rc = strcmp( left->FirstName, right->FirstName );

    if( 0 == rc ) 
        {
        if( left->Age == right->Age )
            rc = 0;

        if( left->Age < right->Age )
            rc = -1;

        if( left->Age > right->Age )
            rc = 1;

        }    /*    if( the first names match )    */

    return rc;

    }
        /*    compareAge()    */
Last edited on
deSertfiSh (6)
thx! I think, I got the idea now and can aplly it on my concret problem!

Thx for answering!

deSertfiSh
vlad from moscow (6539)
kooth,

that do not do three comparisions it is better to add 'else'

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        if( left->Age == right->Age )
            rc = 0;

        else if( left->Age < right->Age )
            rc = -1;

        else if( left->Age > right->Age )
            rc = 1;
kooth (746)
vlad,

Yes, I know: I was trying to get this done quickly. deSertfiSh: You're welcome!
vlad from moscow (6539)
The simplest body of the function is

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int rc;

if ( !( rc = strcmp( left->FirstName, right->FirstName ) ) rc = left->Age - right->Age;

return ( rc );
Last edited on
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