count elements in array not array size

Question

I realized that sizeof(arr)/sizeof(arr[0]) returns the size of the array and not the actual number of elements in the array.

   int main(void) 
{

    int a = 1;
    int b = 2;

    int arr[5] = {a, b};

    int arrcount = sizeof(arr)/sizeof(arr[0]);

    printf("Array Size: %d\n", arrcount);

    return EXIT_SUCCESS;

}

arrcount here equals to 5. Is there a way to get the number of elements equal 2 in this scenario without changing the array size?

It's not clear what you mean by "the number of elements". There are five elements in that array. Do you mean the number of non-zero elements? Maybe you really want std::vector. — David Schwartz
– David Schwartz, Commented Apr 7, 2019 at 5:13
int arr[5] = {a, b}; just remove the 5 here. It is not required when you're assigning to an array literal. — Rafael
– Rafael, Commented Apr 7, 2019 at 5:15
The size of the array and the number of elements are the same. Arrays are fixed size containers. — Galik
– Galik, Commented Apr 7, 2019 at 5:17
Perhaps the container you're looking for is Boost's static_vector? — Qaz
– Qaz, Commented Apr 7, 2019 at 5:18

R Sahu · Accepted Answer · 2019-04-07 05:22:30Z

2

I realized that sizeof(arr)/sizeof(arr[0]) returns the size of the array and not the actual number of elements in the array.

When you say the actual number of elements in the array, I think you mean the number of elements that have been explicitly initialized to something other than zero.

The only way to to do that would be to iterate through the elements of the array and count the number of elements that pass a certain filter.

int count = 0;
for ( int item : arr )
{
  if ( item != 0 ) // This is a filter
    ++count;
}

The standard library provides a function for that, std::count_if.

int count = std::count_if(std::begin(arr), std::end(arr),
                          [](int item) -> bool { return item != 0; });

answered Apr 7, 2019 at 5:22

R Sahu

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