Passing Arrays by Reference

[xantavis]

Does that work? I would like to run some code in the main, then it jumps to a void, where an array is given its ints, then it should return to the int main () where it continues using the array with the ints from the void.

[HiteshVaghani1]

yaa it will work...
suppose your this is your array
int arr[N];
you can call any function
like,
functionName(&arr);
hope, this will help you..

[xantavis]

OK, but can you still give me an example, for it doesnt work in my program

[Moschops]

#include <iostream>

using namespace std;

void doSomething (int* theArray)
{
  theArray[0] = 7;
  theArray[4] = 9;
}

int main()
{
  int arr[10];
  cout << arr[0] << " " << arr[4] << endl;
  doSomething(arr);
  cout << arr[0] << " " << arr[4] << endl;
}

[vlad from moscow]

There are two possibilities: either pass an array by reference or pass an array by value. When an array is passed by value it is converted to the pointer to its first element. I will show two variants.

#innclude <iostream>

void fill( int *a, int n )
{
   for ( int i = 0; i < n; i++ ) a[i] = i;
}

const int N = 10;

void reverse_fill( int ( &a )[N] )
{
   for ( int i = 0; i < N; i++ ) a[i] = N - i - 1;
}

int main()
{
   int a[N];

   fill( a, N );

   for ( int i = 0; i < N; i++ ) std::cout << a[i] << ' ';
   std::cout << std::endl;

   reverse_fill( a );

   for ( int i = 0; i < N; i++ ) std::cout << a[i] << ' ';
   std::cout << std::endl;

   return 0;
}

The difference between the functions is that in the second function that gets the array by reference the size of the array shall be a constant expression. It is why constant N was declared before the function declaration.

[o1vk4iN6]

pass an array by value

Wouldn't it be better to say "array pointer" otherwise to me it sounds like a copy of the array is being made and any modifications won't effect the original.

[vlad from moscow]

@xerzi
Wouldn't it be better to say "array pointer" otherwise to me it sounds like a copy of the array is being made and any modifications won't effect the original.

You are not specifying a pointer as the argument. You are specifying the array which implicitly will be converted to the pointer to its first element.

And I do not know such term as "array pointer". Atl least there is no such a term in the C++ standard.

[o1vk4iN6]

to say you are passing an array by value is poorly worded and easily confused by everyone not living in the subset of c++.

[vlad from moscow]

I do not know also what is "subset of C++". I know C++ and try to use terms that are defined in the C++ standard. I do not bother that somebody who does not live in "the subset of C++" can be confused . Every programming language has its own system of terminolodgy that every one should follow. Moreover this is a forum on C/C++.

And as I menitioned already above there is no such term as "array pointer" in the C++ standard. So it is such a term as "array pointer" that can confuse everybody who knows C++.

[o1vk4iN6]

"pass array by value" is not C++ terminology, it is common amongst all programming languages and describes how an object is to be passed to a function. The only reason this would be meaningful is if you know specifically how c-arrays work, and even still when you say array I would be assuming std::array which would make your examples incorrect with your saying. Use proper terminology: "c-array".

So if you read in the standard there is a teapot orbiting the sun you would believe it, use some of your own brain power.

[vlad from moscow]

@xerzi
when you say array I would be assuming std::array

It is only your personal problem what you are assuming when somebody are speaking about arrays.:)

One more there is no such term as c-array in the C++ Standard. There is term array that denotes a compound type and std::array (I hope you see namespace name std) that denotes a standard template container.
Moreover this theme deals with the compound type array and nobody except you assumed that the author of the theme are speaking about the standard container std::array.

Moreover I'd like to point out that std::array appeared only in C++ 2011 so nobody was confused when somebody was saying about arrays. :)

[o1vk4iN6]

nobody except you

As far as I can tell it's just me and you. So idk who you are talking about other then your imaginary peers.

If I were to say "string", which would you think I am talking about. Think about it, it is related. :)

As such again keep your mind open, the community makes their own distinctions to add clarification to things the standard does not. It is a community driven effort and if all you do is lock yourself in your room then continue.

appeared only in C++ 2011 so nobody (note: only you [vlad]) was confused

Then I suggest you read the new standard and get yourself up-to-date grandpa. :)

[vlad from moscow]

I am sorry I am not a doctor. It is maybe a doctor who will be interesting your problems.

[o1vk4iN6]

I know you are not a physician (unless you mean doctor of computer science, then sorry to hear that), I am trying to help you. You probably don't know what it means to communicate a thought, with clarity, to another person so they can understand you, as you are clearly using google translator with that terrible grammar.