qsort struct not doing as supposed to-CodePudding

Hi so I'm trying to sort my struct with qsort and it sort of works but not really... Can anyone tell me what's happening and why it goes wrong ? :)

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

int el_cmp(const void *ep1, const void *ep2);

typedef struct kort
{
    int kuloer;
    int vaerdi;
} kort;

int main(void){
    int i; 
    int k[] = {3, 4, 5, 6};
    int v[] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14};
    
    kort kort[52];

    for (i = 0; i < 52; i  ){

        kort[i].kuloer = k[i % 4];
        kort[i].vaerdi = v[i % 13];

        
    }
    printf("\n");

    qsort(kort, 52, sizeof(int), el_cmp);
 
    for (i = 0; i < 52; i  ){

        printf("Kort%d: %d %d\n", i   1, kort[i].kuloer, kort[i].vaerdi);
    }
     

    return(0);
}

int el_cmp(const void *ep1, const void *ep2){
    int *tp1 = (int*) ep1,
        *tp2 = (int*) ep2;

    if (*tp1 < *tp2){
        return -1;
    } else if (*tp1 > *tp2){
        return 1;
    } else return 0;
}

the result is this:

Kort1: 2 2

Kort2: 3 3

Kort3: 3 3

Kort4: 3 3

... Kort5: 3 3, Kort6: 3 4, Kort7: 4 4, Kort8: 4 4, Kort9: 4 4, Kort10: 4 4, Kort11: 5 5, Kort12: 5 5, Kort13: 5 5, Kort14: 5 5, Kort15: 6 6, Kort16: 6 6 Kort17: 6 6, Kort18: 6 6, Kort19: 7 7, Kort20: 8 8, Kort21: 9 9, Kort22: 10 10, Kort23: 11 11, Kort24: 12 12, Kort25: 13 13, Kort26: 14 14,

Kort27: 5 2

Kort28: 6 3

Kort29: 3 4

... Kort30: 4 5, Kort31: 5 6, Kort32: 6 7, Kort33: 3 8, Kort34: 4 9, Kort35: 5 10, Kort36: 6 11, Kort37: 3 12, Kort38: 4 13, Kort39: 5 14, Kort40: 6 2, Kort41: 3 3, Kort42: 4 4, Kort43: 5 5, Kort44: 6 6, Kort45: 3 7, Kort46: 4 8, Kort47: 5 9, Kort48: 6 10, Kort49: 3 11, Kort50: 4 12, Kort51: 5 13, Kort52: 6 14,

but I'm expecting this:

Kort1: 3 2

Kort2: 3 3

Kort3: 3 4

Kort4: 3 5

... Kort5: 3 6, Kort6: 3 7, Kort7: 3 8, Kort8: 3 9, Kort9: 3 10, Kort10: 3 11, Kort11: 3 12, Kort12: 3 13, Kort13: 3 14,

Kort14: 4 2

Kort15: 4 3

... Kort16: 4 4, Kort17: 4 5, Kort18: 4 6, Kort19: 4 7, Kort20: 4 8, Kort21: 4 9, Kort22: 4 10, Kort23: 4 11, Kort24: 4 12, Kort25: 4 13, Kort26: 4 14,

... Kort27: 5 2, Kort28: 5 3, Kort29: 5 4, Kort30: 5 5, Kort31: 5 6, Kort32: 5 7, Kort33: 5 8, Kort34: 5 9, Kort35: 5 10, Kort36: 5 11, Kort37: 5 12, Kort38: 5 13, Kort39: 5 14,

... Kort40: 6 2, Kort41: 6 3, Kort42: 6 4, Kort43: 6 5, Kort44: 6 6, Kort45: 6 7, Kort46: 6 8, Kort47: 6 9, Kort48: 6 10, Kort49: 6 11, Kort50: 6 12, Kort51: 6 13, Kort52: 6 14,

CodePudding user response：

For starters it is a bad idea to redeclare the name kort

kort kort[52];

Nevertheless this call of qsort

qsort(kort, 52, sizeof(int), el_cmp);

is incorrect. You have an array of structures of the type struct kort not of the type int. The call of qsort can look the following way

qsort(kort, sizeof( kort ) / sizeof( *kort ), sizeof( *kort ), el_cmp);

The comparison function can look the following way

int el_cmp( const void *ep1, const void *ep2 )
{
    const struct kort *a = ep1;
    const struct kort *b = ep2;

    int result = ( b->kuloer < a->kuloer ) - ( a->kuloer < b->kuloer );

    if ( result == 0 )
    {
        result = ( b->vaerdi < a->vaerdi ) - ( a->vaerdi < b->vaerdi );
    }

    return result;
}

Here is your updated program.

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

typedef struct kort
{
    int kuloer;
    int vaerdi;
} kort;

int el_cmp( const void *ep1, const void *ep2 )
{
    const struct kort *a = ep1;
    const struct kort *b = ep2;

    int result = ( b->kuloer < a->kuloer ) - ( a->kuloer < b->kuloer );

    if (result == 0)
    {
        result = ( b->vaerdi < a->vaerdi ) - ( a->vaerdi < b->vaerdi );
    }

    return result;
}

int main( void )
{
    int k[] = { 3, 4, 5, 6 };
    int v[] = { 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 };

    const size_t k_size = sizeof( k ) / sizeof( *k );
    const size_t v_size = sizeof( v ) / sizeof( *v );

    enum { N = 52 };

    kort kort[N];

    for ( size_t i = 0; i < N; i   ) 
    {

        kort[i].kuloer = k[i % k_size];
        kort[i].vaerdi = v[i % v_size];
    }

    qsort( kort, N, sizeof( *kort ), el_cmp );

    for ( size_t i = 0; i < N; i   ) 
    {
        printf( "Kort%zu: %d %d\n", i   1, kort[i].kuloer, kort[i].vaerdi );
    }
    putchar( '\n' );
}

The program output is the same as you are expecting

Kort1: 3 2
Kort2: 3 3
Kort3: 3 4
Kort4: 3 5
Kort5: 3 6
Kort6: 3 7
Kort7: 3 8
Kort8: 3 9
Kort9: 3 10
Kort10: 3 11
Kort11: 3 12
Kort12: 3 13
Kort13: 3 14
Kort14: 4 2
Kort15: 4 3
Kort16: 4 4
Kort17: 4 5
Kort18: 4 6
Kort19: 4 7
Kort20: 4 8
Kort21: 4 9
Kort22: 4 10
Kort23: 4 11
Kort24: 4 12
Kort25: 4 13
Kort26: 4 14
//...