Unable to Initialize 2D Array

Question

I have declared a 2D global array variable like so:

int grid_2d_array[ROWS][COLUMNS];

then in main I've to initialize it with hard-coded values:

grid_2d_array[ROWS][COLUMNS] = {{5, 7, 2, 8, 3, 6, 1, 4},
                                ....
                                {1, 6, 3, 2, 4, 8, 9, 5}
                                };

Example:

#include <stdio.h>

#define ROWS    9
#define COLUMNS 9

/* Global variable. */
int grid_2d_array[ROWS][COLUMNS];

int main() 
{
   /* Initialze the 2D array. */
   grid_2d_array[ROWS][COLUMNS] = {{5, 7, 2, 8, 3, 6, 1, 4},
                                   ....
                                   {1, 6, 3, 2, 4, 8, 9, 5}
                                  };

   return 0;
}

But when I try compiling the source code, GCC gives the following error:

source_file.c: In function ‘main’:
source_file.c:45:34: error: expected expression before ‘{’ token
 grid_2d_array[ROWS][COLUMNS] = {{5, 7, 2, 8, 3, 6, 1, 4},
                                ^

I'm not sure why GCC is not recognizing grid_2d_array as a global variable.

The problem goes away if I redeclare the aforementioned variable in main.

I'm running GCC version: gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04)

Please provide a proper minimal example of this that others can try to compile. Now it's unclear where the definition is and if something else affects the problem. — Sami Kuhmonen
– Sami Kuhmonen, Commented Oct 6, 2015 at 8:21
You need to allocate memory for your array and its nested arrays. — vdolez
– vdolez, Commented Oct 6, 2015 at 8:21
grid_2d_array[ROWS][COLUMNS] = specifies an element (which does not exist) of the array. Try removing the [ROWS][COLUMNS] and just use grid_2d_array = { /*your stuff goes here*/};. — Evil Dog Pie
– Evil Dog Pie, Commented Oct 6, 2015 at 8:24
Is there any reason why you do not use a std::array<std::array<int>> ? — 463035818_is_not_an_ai
– 463035818_is_not_an_ai, Commented Oct 6, 2015 at 8:24
@tobi303 Good question. Is this C or C++ (it can't be both)? — Evil Dog Pie
– Evil Dog Pie, Commented Oct 6, 2015 at 8:25

FireAphis · Accepted Answer · 2015-10-06 08:27:40Z

5

C and C++ arrays can be initialized only as a part of the definition statement:

int grid_2d_array[ROWS][COLUMNS] = {{5, 7, 2, 8, 3, 6, 1, 4},
                                    ....
                                    {1, 6, 3, 2, 4, 8, 9, 5}
                                   };

Assignment of multiple values into an array is not supported.

answered Oct 6, 2015 at 8:27

FireAphis

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David Ranieri · Accepted Answer · 2015-10-06 08:44:11Z

2

In addition to FireAphis's answer, if you are under C99 you can initialize a pointer to array of ints (not a 2D array) outside his definition using compound literals:

int (*grid_2d_array)[COLUMNS]; /* Pointer to array of n int's */

in main:

grid_2d_array = (int [ROWS][COLUMNS]){
    {5, 7, 2, 8, 3, 6, 1, 4},
    {1, 6, 3, 2, 4, 8, 9, 5}
};

answered Oct 6, 2015 at 8:44

David Ranieri

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