Question

I am supposed to follow the following criteria:

Implement function answer4 (pointer parameter and n):

1. Prepare an array of student_record using malloc() of n items.

2. Duplicate the student record from the parameter to the array n
   times.

3. Return the array.

And I came with the code below, but it’s obviously not correct. What’s the correct way to implement this?

student_record *answer4(student_record* p, unsigned int n)
{
    int i;
    student_record* q = malloc(sizeof(student_record)*n);
    for(i = 0; i < n ; i++){
        q[i] = p[i];
    }
    free(q);
    return q;
};

Answer 1

p = malloc(sizeof(student_record)*n);

This is problematic: you’re overwriting the p input argument, so you can’t reference the data you were handed after that line.

Which means that your inner loop reads initialized data.

This:

return a; 

is problematic too – it would return a pointer to a local variable, and that’s not good – that pointer becomes invalid as soon as the function returns.

What you need is something like:

student_record* ret = malloc(...);

for (int i=...) {
 // copy p[i] to ret[i]
}

return ret;