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#include <iostream>
using namespace std;


int function(int arr [])
{
  int y = sizeof(arr)/sizeof(arr[0]);
  return y;
}

int main ()
{
  int arr[] = {1,2,3,4,5,6};

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

  cout <<x<<"\n";

  int y=function(arr);

  cout <<y<<"\n";

  return 0;
}
Hristo Iliev
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Om Prakash Kumar
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  • So what output are you getting? – striving_coder Nov 22 '14 at 14:17
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    `[]` in a function parameter does not mean an array, it means a pointer. – The Paramagnetic Croissant Nov 22 '14 at 14:19
  • @TheParamagneticCroissant - in my opionion, om gupta wants write a function where the calculation of the array length is done via a function and I do not know a way how to do that. I would say, this is not possible, because the calculation is done in the preprocessor. Am I correct? – lx42.de Nov 23 '14 at 12:12
  • @Mat how did you add the `This question already has an answer here:`, I found another very good answer: http://stackoverflow.com/questions/4162923/calculate-length-of-array-in-c-by-using-function – lx42.de Nov 23 '14 at 12:26
  • @lx42.de it's not possible. The calculation is not done by the preprocessor either. – The Paramagnetic Croissant Nov 23 '14 at 13:34
  • @lx42.de, the message at the top is automatically added by Stack Overflow when the question is closed for being a duplicate of another one. – Hristo Iliev Nov 24 '14 at 14:32

2 Answers2

1
  int arr[] = {1,2,3,4,5,6};
  int x = sizeof(arr)/sizeof(arr[0]);

In this case arr is an array of 6 int elements. sizeof of an int is 4 bytes, thus sizeof(arr) is 24, divided by sizeof of a single int equals 6.

int function(int arr [])
{
  int y = sizeof(arr)/sizeof(arr[0]);
  return y;
}

In this case arr decays to a pointer to an int. Depending on your platform, sizeof of a pointer might be 4 or 8 bytes.

Jiří Pospíšil
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0

The output will be as follows:

6
1

Explanation:

When you compute x inside the main() function, arr is an array. Therefore, sizeof(arr) returns the size of the whole array in bytes.

int x = sizeof(arr) / sizeof(arr[0]);
// 24 / 4 = 6 (assuming your compiler assigns 4 bytes to an integer)

But when you pass the same to a function, what gets passed as the parameter is the pointer to the array. So, this is essentially like passing int *arr to the function.

Source: C++ Size of Array

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pradeepcep
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  • I got 6 and 2 on cygwin: PE32+ executable (console) x86-64, for MS Windows. My integers are 64bit/8 Byte long. – lx42.de Nov 23 '14 at 12:19