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Passing argument 4 of qsort from an incompatible pointer type

I am having problems with the function we have to write. Presumably, this is how it should work, but it gives me an incompatible error like a pointer, and I'm not sure how to fix it.

The problem is qsort referencing the compare_last function.

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

#define MAX_PERSONS 100

//person structure definition goes here
typedef struct{
    char last[32];
    char first[32];
    int year;
}Person;

//function declarations go here
int compare_last(Person * ptr1, Person * ptr2);

void main(void){//main function goes here
    char *infilename[20];
    char *outfilename[20];
    FILE * fptrin;
    FILE * fptrout;
    int i, j;
    Person musicians[MAX_PERSONS];
    printf("Enter input file name: ");
    scanf("%s", infilename);
    printf("Enter output file name: ");
    scanf("%s", outfilename);
    strcat(*outfilename, ".htm");
    fptrin = fopen(*infilename, "r");
    fptrout = fopen(*outfilename, "w");

    for(i = 0; i < MAX_PERSONS; i++)
    {
        fscanf(fptrin, "%s %s %i", musicians[i].last, musicians[i].first, &musicians[i].year);
    }

    qsort(musicians, i, sizeof(musicians[0]), compare_last);

    fprintf(fptrout, "<html>\n<body>\n<title>LAB14</title>\n");

    for(j = 0; j < i; j++)
    {
        fprintf(fptrout, "%s %s %i <br>", musicians[j].last, musicians[j].first, musicians[j].year);
    }

    fprintf(fptrout, "</body>\n</html>\n");
    fclose(fptrin);
    fclose(fptrout);

}//end main

//function definitions go here

int compare_last(Person * ptr1, Person * ptr2)
{
    int result = strcmp(ptr1 -> last, ptr2 -> last);
    if(result != 0)
        return result;
    else
        return strcmp(ptr1 -> first, ptr2 -> first); 
}
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2 answers
int compare_last(Person * ptr1, Person * ptr2);

it should be

int compare_last(void * ptr1, void * ptr2);

Then you need to turn on compare_last

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The prototype for qsort()is:

void qsort(void *base, size_t nmemb, size_t size,
           int(*compar)(const void *, const void *));

So your sort function must either match int(*compar)(const void *, const void *), or you need to use qsort () when calling.

Person*, - , :

static int compare_last(const void *ptr1, const void *ptr2)
{
    const Person *p1 = ptr1, *p2 = ptr2;
    int result = strcmp(p1 -> last, p2 -> last);
    ...
}

, const void * const Person *.

+2

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