Converting NSArray to char** and returning the c array

Question

I need to convert an NSarray filled with NSStrings and return this c array to the function.

-(char**) getArray{
        int count = [a_array count];
        char** array = calloc(count, sizeof(char*));

        for(int i = 0; i < count; i++)
        {
             array[i] = [[a_array objectAtIndex:i] UTF8String];
        }
        return array;     
}

I have this code, but when should i free the memory if I'm returning stuff?

in getArray definition you are missing parenthesis (), am i right ? — Omkant
– Omkant, Commented Oct 25, 2012 at 8:59
Lot many things are not clear here .. what is a_array ? and if you are putting characters in array[i] then you have to allocate memory for each array[i] also — Omkant
– Omkant, Commented Oct 25, 2012 at 9:03

trojanfoe · Accepted Answer · 2012-10-25 09:06:04Z

5

You need to allocate memory for each string in the array as well. strdup() would work for this. You also need to add a NULL to the end of the array, so you know where it ends:

- (char**)getArray
{
    unsigned count = [a_array count];
    char **array = (char **)malloc((count + 1) * sizeof(char*));

    for (unsigned i = 0; i < count; i++)
    {
         array[i] = strdup([[a_array objectAtIndex:i] UTF8String]);
    }
    array[count] = NULL;
    return array;     
}

To free the array, you can use:

- (void)freeArray:(char **)array
{
    if (array != NULL)
    {
        for (unsigned index = 0; array[index] != NULL; index++)
        {
            free(array[index]);
        }
        free(array);
    }
}

edited Oct 25, 2012 at 9:06

answered Oct 25, 2012 at 9:00

trojanfoe

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1 Comment

Fast Engy Over a year ago

getArray function should be changed to -(char**)getArray:(NSArray*)a_array{} to pass in the array name

Omkant · Accepted Answer · 2012-10-25 09:04:49Z

1

array you return will be caught in some char** identifier in calling environment of getArray() function using that you can free the memory which you have allocated using calloc() inside getArray() function

int main()
{
 char **a=getArray();
 //use  a as your requirement
 free(a);
}

edited Oct 25, 2012 at 9:04

answered Oct 25, 2012 at 8:56

Omkant

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2 Comments

marcg11 Over a year ago

Oh so the freeing is outside of the function. So much time in objective-c that i forget everything in C...TT

Omkant Over a year ago

Yeah you can free outside because the outside identifier itself pointing to the same memory on heap which you have allocated using calloc....

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