CODEWITHSUNDEEP
cmultidimensional-array
ios developer
ios developer

Reputation: 3473

Return 2 dimension array in C function

I want to write a function in C language which returns the 2 dimension array to my main function.

Upvotes: 1

Views: 8227

Answers (4)

Constantinius
Constantinius

Reputation: 35089

A function that returns a dynamically allocated two dimensional array for the int type.

int ** myfunc(size_t width, size_t height) 
{
    return malloc(width * height * sizeof(int));
}

It has to be deleted with free once it is not used anymore.

EDIT This only allocates the space for the array which could be accessed by pointer arithmetic but unfortunately not by the index operators like array[x][y].

If you want something like this here is a good explanation. It boils down to something like this: 

int ** myfunc(size_t ncolumns, size_t nrows)
{
    int **array;
    array = malloc(nrows * sizeof(int *));
    for(i = 0; i < nrows; i++)
    {
        array[i] = malloc(ncolumns * sizeof(int));
    }
}

Upvotes: 4

asaelr
asaelr

Reputation: 5456

If you know the size of the array, you can do so:

int (*myfunc())[10] {
 int (*ret)[10]=malloc(10*10*sizeof(int));
 return ret;
}

This function return pointer to 10 arrays of 10 ints.

Of course, you should use it as it is, and don't forget to free it after using.

Upvotes: 1

foo
foo

Reputation: 387

You can not simply return malloc( x * y * sizeof(type) );

This will produce a segmentation fault when you try to index the array as a 2 dimensional array. 

int **a = malloc(10 * 10 * sizeof(int));

a[1][0] = 123;
a[0][1] = 321;

The result of the above: Segmentation fault

You need to first create an array of pointers with c/malloc() then iterate this array of pointers and allocate space for the width for each of them. 

void *calloc2d(size_t x, size_t y, size_t elem_size) {
    void **p = calloc(y, sizeof(void*));
    if(!p) return NULL;

    for(int i = 0; i < y; i++) {
        p[i] = calloc(x, elem_size);
        if(!p[i]) {
            free2d(y, p);
            return NULL;
        }
    }

    return (void*)p;
}

And free

void free2d(size_t y, void *matrix) {
    if(!matrix) return;

    void **m = matrix;
    for(int i = 0; i < y; i++) {
        if(m[i]) free(m[i]);
    }
    free(m);

    return;
}

Upvotes: 4

Shashank Kadne
Shashank Kadne

Reputation: 8101

It should be simple i guess...

char **functioName(char param[][20])
{
  char[][20] temp = malloc(20 * 20 * sizeof char);


 //processing  
  return temp

}

Upvotes: 1

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