I can't figure out how to fill an array

Question

I am trying to fill a given array with a passed in value so if I wanted an array to be all 12's it would simply replace all the elements with 12s. The prototype I have for this function looks like this:

void fill(T *left, T *end, T fill)

The driver for this function looks like this:

static void TestFill1(void)
{
   cout << "***** Fill1 *****" << endl;
   int i1[10];
   int size = 10;

   fill(i1, i1 + size, 12);
   display(i1, i1 + size);
}

I am having a problem where I am given an array that is uninitialized. Previously in the assignment I was going through the array until the end. In this case I am given an uninitialized array which makes my T *end the same as T *left. I'm not familiar with a way to go through the passed in array.

I was trying something that looked like this:

template <typename T>
void fill(T *left, T *end, T fill)
{
  int i =  sizeof(*left) / sizeof(*(left + 0));

  while(*(left + i) != *end)
  {
    *(left + i) = fill;
    ++i;
  }
}

I'm not allowed to use subscripts or for loops for this assignment also, #include is off limits same with std::vector.

Answer 1

The variable i, which represents the offset with respect to the first element, should start at zero:

int i = 0;

The loop condition is checking whether the value of the array element is equal to the value of the array element at the end.

while(*(left + i) != *end)

The correct version is the following:

while(left + i != end)

which checks if the pointer (left + i) has reached the end.

Answer 2

Your statement

int i =  sizeof(*left) / sizeof(*(left + 0));

might not do, what you think it does.

The sizeof() function doesn't work on plain pointers the same way as for array declarations:

size_t s = sizeof(*left); // Will evaluate to sizeof(T)

while

int i1[10];
size_t s = sizeof(i1); // Will evaluate to sizeof(int) * 10

Your code can be simply fixed as follows:

template <typename T>
void fill(T *left, T *end, T fill) {
    T* cur = left;

    while(cur < end) {
       *cur  = fill;
       ++cur;
    }
}

Answer 3

http://www.cplusplus.com/reference/vector/vector/assign/

#include <vector>

int main ()
{
  std::vector<int> first;

  first.assign (10,12);  // 10 ints with a value of 12
  return 0;
}

This is how real men do it ™. lol sorry I couldn't resist.