Passing array to function with dynamic declaration of array in C/C++

Question

I want to pass array to function in C/C++ without declaring and assigning it previously. As in C# we can:

fun(new int[] {1, 1}); //this is a function call for void fun(int[]) type function

I am not very sure about the correctness of the above code. But I had done something like this in C#.

How can we pass array to function using dynamic declaration (on the spot declaration)??

I'd tried it using following way. But no luck

fun(int {1,1});
fun(int[] {1,1});
fun((int[]) {1,1});

can't we do so..??

Why the turbo-c and turbo-c++ tags? Do you use those compilers? — RedX
– RedX, Commented Jul 21, 2012 at 10:21
Do you want a C or a C++ solution? This makes a significant difference here. — Björn Pollex
– Björn Pollex, Commented Jul 21, 2012 at 10:32

Oliver Charlesworth · Accepted Answer · 2012-07-21 10:31:14Z

4

In C99 and later, this:

foo((int[]){2,4,6,8});

is approximately the same as this:

int x[] = {2,4,6,8};
foo(x);

Prior to C99, this is not possible. C++ does not support this syntax either.

edited Jul 21, 2012 at 10:31

answered Jul 21, 2012 at 10:24

Oliver Charlesworth

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5 Comments

Oliver Charlesworth Over a year ago

@ShashwatTripathi: C99 is the second most recent version of the C language, which Turbo-C probably doesn't support.

shashwat Over a year ago

and what about Borland C/C++ compiler..??

Oliver Charlesworth Over a year ago

@ShashwatTripathi: That's a very ancient compiler as well. I suggest moving to a modern development environment.

shashwat Over a year ago

Actually I was solving some previous year Question Paper for my practical exam of C++. They provide Turbo and Borland compilers only. That's why i was finding a solution for that. But now I'd know, I have to declare it before passing.

fredoverflow Over a year ago

You can download several C++ IDEs for free. I recommend CodeLite.

fredoverflow · Accepted Answer · 2012-07-21 11:28:38Z

3

In C++11, you can use an initializer list:

#include <initializer_list>
#include <iostream>

void fun(std::initializer_list<int> numbers)
{
    for (int x : numbers)
        std::cout << x << ' ';
    std::cout << '\n';
}

int main()
{
    fun( {2, 3, 5, 7, 11, 13, 17, 19} );
}

answered Jul 21, 2012 at 11:28

fredoverflow

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Comments

alinsoar · Accepted Answer · 2012-07-21 10:29:53Z

2

This is possible in ANSI C99 and C11, but not in C89.

answered Jul 21, 2012 at 10:29

alinsoar

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Comments

ATaylor · Accepted Answer · 2012-07-21 10:38:15Z

1

May I suggest using a variable argument list?

The declaration syntax would be as follows:

void Function(int Count, ...) {
     va_list va;
     va_start(va, Count);
     for(int i = 0; i < Count; ++i) {
         int nextVar = va_arg(va, int);
         //Do some stuff with the array element
     }
     va_end(va);
}

This function is called with:

Function(4, 2, 3, 1, 5);

2, 3, 1 and 5 are the 'array elements'.

Alternatively, if you 'need' an array to go through within that function, it's easy to move the variable list to a proper (dynamic) array, by using new and delete.

Within the va-function:

 int *Array = new int[Count];
 for(int i = 0; i < Count; ++i) {
      Array[i] = va_arg(va, int);
 }
 //Do Stuff with Array
 delete[] Array;

edited Jul 21, 2012 at 10:38

answered Jul 21, 2012 at 10:30

ATaylor

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3 Comments

ATaylor Over a year ago

It should work. It's standard C, as far as I know and is the only way that comes to mind, to pass an 'array' without initializing one first. Why don't you just give it a go and see if it works as you expect it to?

ATaylor Over a year ago

@alinsoar Actually it's not a different problem...the problem is, that he wants to pass a variable number of elements of the same type, without having to initialize an array of that type prior to the function. As such, the variable argument list is a valid solution for the problem.

alinsoar Over a year ago

Yes. The problem is * pass a parameter without having declared it *. The problem is clear.

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