How to pass array in C++

Question

I trying to pass an array but don't understand why it gives me those errors. The code is also available in ideone.com

#include <iostream>

using namespace std;

class Max
{
   int max = 0;

   public:
      int getMax(int array[], int size)
      {
          for(int num : array)
          {
                if(num > max)
                    max = num;
          }
          return max;
      }
};

int main( )
{
   Max m;
   int arr[5] = { 5, 3, 2, 7, 6 };
   cout << "Max number is: " << m.getMax(arr,5);

   return 0;
}

The easiest way is to take a `std::array` or something like `std::vector`. Everything will just work. No implicit decaying to a pointer. No size information loss. — chris, Jun 13 '13 at 03:11
use containers (e.g. vectors) if you can. Life will be easy :) — Bill, Jun 13 '13 at 03:12

score 1 · Answer 1 · edited May 23 '17 at 12:21

1

The problem here as has been mentioned is that passing an array to a function it decays to a pointer. The fix that involves the least changes is to pass the array by reference like so:

template <int U>
int getMax(int (&array)[U])

this fix is probably not the most intuitive for a beginner though. The fix that requires a bit more changes and probably makes more sense to a beginner is to use std::vector or std::array:

int getMax(const std::vector<int> &array)

and in main:

std::vector<int> arr = { 5, 3, 2, 7, 6 };
cout << "Max number is: " << m.getMax(arr);

edited May 23 '17 at 12:21

Community

1
1

answered Jun 13 '13 at 03:34

Shafik Yaghmour

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const reference would be better than passing `vector` by value. – n0rd Jun 13 '13 at 16:42

n0rd · Answer 2 · 2013-06-13T16:44:17.117

0

size argument needs type specified (proper type is size_t).
array in getMax function is a pointer (not an array). You can't use range-based for loop with it. You have to use regular for loop which will make use of size argument.

edited Jun 13 '13 at 16:44

answered Jun 13 '13 at 03:14

n0rd

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The issue is that the method does not receive an array *at all*. You cannot pass arrays to functions; they decay to a pointer. – Ed S. Jun 13 '13 at 03:16
1

I figure you know that, but I don't think the OP does. – Ed S. Jun 13 '13 at 03:18
I know that size must have int.. i just missed it.. what i can do instead? can you show me in code? – a1204773 Jun 13 '13 at 03:19
I fixed it but it still doesn't compile.. can you please check the ideone link? – a1204773 Jun 13 '13 at 03:26
You didn't fix everything. You still use wrong type of `for` loop. – n0rd Jun 13 '13 at 03:31

score 0 · Answer 3 · answered Jun 13 '13 at 03:40

The cause is the for(:) can not get the size of "int array[]".

You have a size argument, but the begin() & end() can not use it. You must wrap the begin() and end() member functions or just simple it to

for(int i = 0; i< size; i++)
{
   int num = array[i];
   if(num > max)
      max = num;
}

How to pass array in C++

3 Answers3