CODEWITHSUNDEEP
cfunctionstructure
Coder123
Coder123

Reputation: 854

qsort doesnt change my array order

i have an array of structures (Employee):

typedef struct Employee{
    char name[MAX_SIZE];
    int salary;
    int experience;
} employee_t;

i want to reorder my array by salary, i have created a comperator:

int compareEmployeesBySalary(const void* a, const void* b){
        employee_t* one = (employee_t*)a;
        employee_t* two = (employee_t*)b;

        if (one->salary == two->salary)
            return 0;
        else if (one->salary > two->salary)
            return 1;
        else
            return -1;
    }


void main()
{
    int i;

    employee_t** employeeArray = (employee_t**)malloc(sizeof(employee_t*)*5);

    for(i=0 ; i < 2 ; i++)
    {
        employeeArray[i] = (employee_t*)malloc(sizeof(employee_t));
        readEmployee( employeeArray[i] ); //input for 5 employee's
    }

    puts("");
    puts("beforesort\n");
    for(i=0; i <2 ; i++)
    {
        printEmployee(employeeArray[i]);
    }
    puts("--------------------------------------------------------");
    puts("after salary sort\n");

    qsort(&employeeArray, 2, sizeof(employee_t), compareEmployeesBySalary);
    for(i=0; i < 2 ; i++)
        printEmployee( employeeArray[i] );
}

when i run it normally it just prints the original array by the order i insert the employees, but when im debugging it prints by my compare function, why is that?

thank you!!!

Upvotes: 0

Views: 254

Answers (2)

Filipe Gon&#231;alves
Filipe Gon&#231;alves

Reputation: 21213

You need to change this:

qsort(&employeeArray, 2, sizeof(employee_t), compareEmployeesBySalary);

To:

qsort(employeeArray, 2, sizeof(employee_t *), compareEmployeesBySalary);

The first argument must be employeeArray because the qsort() function receives a pointer to the start of the array, not a pointer to a pointer to the start of the array. Plus, you have an array of pointers, not an array of employee_t, so the 3rd argument must be sizeof(employee_t *).

Finally, change your compare function to:

int compareEmployeesBySalary(const void* a, const void* b){
        employee_t* one = *(employee_t **)a;
        employee_t* two = *(employee_t **)b;

        if (one->salary == two->salary)
            return 0;
        else if (one->salary > two->salary)
            return 1;
        else
            return -1;
}

Because again, what you have is an array of pointers, so a and b will be of type employee_t **.

Upvotes: 5

James Linnell
James Linnell

Reputation: 3834

One thing I see is that you pass sizeof(employee_t) into the size parameter of qsort, whereas your array only stores pointers to employee_t. I suggest you try replacing sizeof(employee_t) in qsort with sizeof(employee_t*).

Upvotes: 0

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