Thread: Passing two-dimensional arrays to functions

Hello everyone, I'm trying to send a non-const two-dimensional array to a function that receives it as const 2-dimensional array, but the compiler (GNU GCC Compiler) issues the following warning in the function call:

" warning: passing argument 1 of 'receiveArray' from incompatible pointer type ".

Also, it issues the following warning in the function prototype:

" note: expected 'const int (*)[2]' but argument is of type 'int (*)[2]' ".

The code is:

Code:

#include <stdio.h>

/* Function prototype: */
void receiveArray(const int array_copy[][2]);

int main(void)
{
    int array[2][2] = { { 2, 1 }, { 1, 4 } };

    receiveArray(array);

    return 0;
}

void receiveArray(const int array_copy[][2])
{
    printf("Array received successfully.\n");
}

If I declare array as const int, the program is compiled without warning - so, is there a way to send a non-const double-subscripted array to a function and that function to receive it as const? I know it is possible with 1-dimensional arrays. Thanks in advance!

I think you should change your function so you can pass in what you need to pass. The array_copy variable is a pointer to an array so that is why it is treated differently than what you're used to. If the compiler didn't give this warning, it would mean that you could use constless pointers to modify const variables.

Originally Posted by Ocifer

I actually tried compiling the code you provided and it worked without any problems. Not sure exactly why ? I compiled with -Wall on gcc.

EDIT: was using code::blocks and mingw on winows, upon switching to Linux terminal and gcc it gives the error. Not sure what's up. Hopefully someone else will know.

Thanks for testing. I am using Code::Blocks with mingw too, in Windows XP - is it possible that there might be something wrong with my computer?

Originally Posted by whiteflags

I think you should change your function so you can pass in what you need to pass. The array_copy variable is a pointer to an array so that is why it is treated differently than what you're used to. If the compiler didn't give this warning, it would mean that you could use constless pointers to modify const variables.

Thanks, whiteflags, but how is it possible that I can make the passing I'm trying to make with 1-dimensional arrays?

Hi, Ocifer, thanks for the help. I'm not trying to change the array within the function, but this doubt came up when I was doing another program larger than the one I've written in here. Anyway, I'll try to find out more about the const qualifier.