How to return an array from a function

This is a discussion on How to return an array from a function within the C Programming forums, part of the General Programming Boards category; I'm relatively new to C and I'm having trouble returning an array from a function. Apologies if this have been ...

  1. #1
    Registered User
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    Sep 2009
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    How to return an array from a function

    I'm relatively new to C and I'm having trouble returning an array from a function. Apologies if this have been answered elsewhere but I can't find it. I read somewhere about returning the first element and using a pointer to find the the other elements.

    A simplified version of my code is:

    Code:
    int main()
    {
      int array[3];
      array[0] = func(); 
    }
    
    int func()
    {
      static int array[3];
      array[0]=5;
      array[1]=6;
      array[2]=7;
    
      return array[0];
    }
    This returns the first element but I don't know how to return the other elements.

  2. #2
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    Dnipropetrovsk, Ukraine
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    Hi,
    I'm new to C as well. Sorry if my suggestion turns out to be wrong.
    As far as I understand, for a function to return an array it should be declared as returning a pointer to a desired type, in your code to a type int. (e.g int * func(void))
    The return statement should be something like (return array). The name of an array is a pointer to the 1st element of an array.
    It probably defies the purpose of your task, but you may want to consider the following code:

    Code:
    #include <stdio.h>
    
    #define SIZE 3
    
    /* function prototype; ar[] being a pointer to type int;
     * n being array size */
    void func(int ar[], int n);
    
    int main(void)
    {
    	int i;	/* counter variable */
    
    	/* declare an array of 3 ints */
    	int array[SIZE];
    
    	/* call func() to initialise array[]; pass array name, itself a pointer and
             * an array size */
    	func(array, SIZE);
    
      	/* print contents of array */
    	for (i = 0; i < SIZE; i++)
    		printf("%d ", array[i]);
    	printf("\n");
    
    	return 0;
    }
    
    void func(int ar[], int n)
    {
    	int i;
    	for (i = 0; i < n; i++)
    		ar[i] = i + 5;	/* any other numbers desired */
    }
    You may also want to see this link for an answer to how to return arrays from functions.
    Last edited by sashaKap; 01-26-2010 at 06:42 AM.

  3. #3
    Registered User
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    399
    You can return a pointer to the array. If the array is not static within the function, you must return a dynamically allocated array instead.

    Code:
    int *func_static(void)
    {
            static int arr[5] = {0};
            return arr;
    }
    
    int *func_dynamic(void)
    {
            int *arr = malloc(5 * sizeof(int));
            return arr;
    }

  4. #4
    C++まいる!Cをこわせ!
    Join Date
    Oct 2007
    Posts
    23,014
    Of course, if you use dynamic memory as in the second example, you must free it. Therefore, the preferred way of doing this is doing it like in sashaKap's example.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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