Function return table

Question

Is it possible in C to make an empty 2D array with known number of rows and columns in the main.

e.g. int my_array[10][10]

then pass it in a function (empty):

my_function(r,c,my_array) in order to perform some operations and full the 2D array and return it full in the main?

If yes: I have to malloc-ed? dynamically right? and "free" in main? I use void or return my_array? I have found some examples in the internet and I have been confused. Is there any example to have as guide?

Please show the whole but minimal code that you have tried. There is no such thing as an "empty" or "full" array: every element has *some* value whether or not you explicitly assign values. — Weather Vane, Sep 29 '16 at 19:24
You will find the answer by minimal search effort and in a good C book. The latter might require understanding fundamental concepts of C, though... — too honest for this site, Sep 29 '16 at 19:25
Possible duplicate of [Pass 2D array to function by reference](http://stackoverflow.com/questions/11862054/pass-2d-array-to-function-by-reference) — tinman, Sep 29 '16 at 19:26
@tinman: C does not support references and that question is about a jagged array which is not and cannot be a 2D array. But to me OP is confused at multiple levels. — too honest for this site, Sep 29 '16 at 19:28
@WeatherVane I am sorry I mean that I create for example: a table of 10 rows and 10 columns type of int but I don't have assign yet values. e.g I only defined the table int my_array[10][10]; not assign values. — Giannis Kalamaras, Sep 29 '16 at 19:34
@Olaf: I do not see why the Q I linked to is about jagged arrays and the poster in that Q wants to pass by reference, which is a suitable name for not passing by value. No mention of references in the c++ sense. — tinman, Sep 29 '16 at 19:38
@tinman: You cannot other than pass by value in C! A pointer is a first-class object. Major problem is something like `int **` **cannot** point to a 2D array! — too honest for this site, Sep 29 '16 at 19:41

dbush · Answer 1 · 2016-09-29T19:39:28.787

1

When you define variable like this:

int my_array[10][10];

It creates a 2D array of integers. There is nothing to malloc or free when you do this.

You would declare myfunction as follows:

void myfunction(int r, int c, int array[r][c])

Then inside of this function you can modify array and the the changes would be viewable in the calling function.

Note that this syntax uses a variable sized array parameter based on the other two parameters.

EDIT:

Here's an example of how you could use this:

void initialize(int r, int c, int array[r][c])
{
    int i,j;
    for (i=0;i<r;i++) {
        for (j=0;j<c;j++) {
            array[i][j] = 0;
        }
    }
}

int main()
{
    int my_array[10][10];

    initialize(10,10,my_array);

    // my_array now contains all zeros
    ...
    return 0;
}

edited Sep 29 '16 at 19:39

answered Sep 29 '16 at 19:25

dbush

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Just another one: as we already pass both dimensions (which I support), it might be easier to use array notiation with both dimensions give. I'm aware this is mostly a matter of style, but it documents the intention better imo. – too honest for this site Sep 29 '16 at 19:30
@dbush the definition is inside the main. I call a function inside the main and pass as argument the table to a function in order to perform some operations.. any help? – Giannis Kalamaras Sep 29 '16 at 19:36
@GiannisKalamaras: Yes, and? What's the problem? No offence, but you seem to missed some required prerequisites of C programming. – too honest for this site Sep 29 '16 at 19:39

Function return table

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