I'm trying to sort an array of struct records. For some reason a core dump keeps occuring.
When I try doing the same thing with an array of ints or structs, it works perfectly fine. However when I start using nested structs, it begins to core dump.
The current output is:
Before sorting
first last 0
first last 1
first last 2
first last 3
first last 4
first last 5
AFTER sorting
Segmentation fault (core dumped)
Compiler: Cygwin
typedef struct {
char last[NAMESIZE]; /* last name (1 word) */
char first[NAMESIZE]; /* first name (1 word) */
} name;
typedef struct {
name name;
int score; /* score (between 0 & 100 inclusive) */
} record;
int compare (const void * a, const void * b){
const record *recordA = (record *)a;
const record *recordB = (record *)b;
printf("%d: %d", recordA->score, recordB->score);
return ( recordB->score - recordA->score );
}
int main (){
record ** list;
int i;
list=malloc(6*sizeof(record*));
printf("Before sorting\n");
for(i=0; i<6; i++){
list[i]=malloc(sizeof(record));
strcpy(list[i]->name.first,"first");
strcpy(list[i]->name.last,"last");
list[i]->score=i;
}
for (i=0; i<6; i++){
printf ("%s %s %d\n",list[i]->name.first, list[i]- >name.last,list[i]->score);
}
printf("AFTER sorting\n");
qsort (list, 6, sizeof(record), compare);
for (i=0; i<6; i++){
printf ("%s %s %d\n",list[i]->name.first, list[i]- >name.last,list[i]->score);
}
return 0;
}
list
is an array of 6 pointers to record
:
list=malloc(6*sizeof(record*));
so you need to pass the same size to qsort
.
qsort (list, 6, sizeof(record), compare);
should be
qsort (list, 6, sizeof(record*), compare);
or better yet
qsort (list, 6, sizeof(*list), compare);
I'm agree with the first answer.But one thing clear is that you should not use qsort (list, 6, sizeof(record), compare) , in which sizeof(record) will return the total bytes of record but do not automatically count the bytes used by the name. nor qsort (list, 6, sizeof(record), compare) , in which sizeof(record) will return the 4 bytes of record*,since it's a pointers. Instead, I think maybe you just need count the bytes by your self and add another data,like namesize, in your data structure record
If you have a comparison function for two records, you want to assign them to a pointer to a constant that points to a record.
In your qsort, I'm guessing you've passed in your record list data structure, so the number of elements will be your nused.
/*Comparison function: Score ascending only.*/
int cmp_sasc(const void *p, const void *q){
record * const *pp = p;
record * const *qq = q;
return (*pp)->score - (*qq)->score;
}
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