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Retrieving struct from array of struct in C for qsort


Retrieving struct from array of struct in C for qsort

By : user2948620
Date : November 14 2020, 04:51 PM
I wish did fix the issue. The problem is that your typedef defines test as a pointer type, not a plain type. Then test* becomes a double-pointer, i.e. struct test**. When you write first->data1, you are applying -> operator to a pointer to pointer to struct test, which is not a pointer to a struct.
Since test* is a double-pointer, you need to rewrite your comp to dereference it once before obtaining a member, as follows:
code :
int comp (const void *a, const void* b){
    const test* first = (const test*)a;
    const test* second = (const test*)b;
    return (*first)->data1 - (*second)->data1;
}


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qsort of struct array not working

qsort of struct array not working


By : Djhay
Date : March 29 2020, 07:55 AM
help you fix your problem I am trying to sort a struct run array called results by a char, but when I print the array, nothing is sorted. Have a look at this:
code :
int count_number_of_different_persons(run results[])
run *run1 = *(run **)a;
run *run1 = (run*)a;
How to qsort an array of struct

How to qsort an array of struct


By : SQL database guy
Date : March 29 2020, 07:55 AM
To fix this issue So I was tasked with grabbing a binary file, reading it into an array composed of structs then sorting it based on an array within the struct. The part that I'm stuck on is the sorting. I'm not sure if I'm supposed to sort it as an array (since the binary file is now an array) or sort it as a struct. Heres part of my code bellow. , First off, the comparator function should have the signature:
code :
int compare(const void *v1, const void *v2);
    const FLIGHT *ia = (FLIGHT *)v1;
    const FLIGHT *ib = (FLIGHT *)v2;
    int rc;

    if ((rc = strcmp(ia->OriginCode, ib->OriginCode)) != 0)
        return rc;
    if ((rc = strcmp(ia->DestinationCode, ib->DestinationCode)) != 0)
        return rc;
    …
    return 0;  // Only if the two entries compare as identical
C/C++ qsort an array of struct within a struct

C/C++ qsort an array of struct within a struct


By : Bigozz
Date : March 29 2020, 07:55 AM
around this issue I solved: The problem was the algorithm and the fields of struct edge were not pointers:
Changed that:
code :
 typedef struct EDGE {
    NODE source;
    NODE destination;
    int weight;
} EDGE;
typedef struct EDGE {
    NODE *source;
    NODE *destination;
    int weight;
} EDGE;
for (int e = 0; e < E; e++) {
    if (findSet(graph->edge[e].source)->data != findSet(graph->edge[e].destination)->data) {
        result[resultE++] = graph->edge[e];
        unionSet(graph->edge[e].source,graph->edge[e].destination);
    }
}
qsort an array of structs in a struct

qsort an array of structs in a struct


By : Và tôi yêu em
Date : March 29 2020, 07:55 AM
I wish this help you I'm attempting to sort an array of structs in a struct based on an int value. I've successfully sorted an array of structs but I'm guessing I'm passing a wrong value somewhere for the nested structs. , There are two mistakes with your code
using qsort on a nested struct array

using qsort on a nested struct array


By : user3718171
Date : March 29 2020, 07:55 AM
I hope this helps you . If you want to sort the elements in the List array using qsort, then do e.g.
code :
qsort(Users[nInd].List, NumberOfElementsInList, sizeof(struct items), CompareItems);
int CompareItems(const void *a, const void *b)
{
    const struct items *item_a = (const struct items *) a;
    const struct items *item_b = (const struct items *) b;

    if (item_a->nID > item_b->nID)
        return 1;
    else if (item_a->nID < item_b->nID)
        return -1;
    else
        return 0;
}
if (Users[nInd].List[0].nID > Users[nInd].List[1].nID)
{
    // Swap the items as index 0 and 1, thereby sorting them
    struct items temp_item = Users[nInd].List[0];
    Users[nInd].List[0] = Users[nInd].List[1];
    Users[nInd].List[1] = temp_item;
}
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