int data[4][3] = 
{1, 2,3,
4,5,6,
7,8,9,
10,11,12
};

size_t obj_size = sizeof(int);
size_t obj_cnt = 12;
char *filename= "output.dat";
FILE *p_file;

p_file=fopen(filename,"w");
fwrite(&data, obj_size, obj_cnt, p_file);
fclose (p_file);

kenkoh.c: In function ‘main’:
kenkoh.c:17: warning: missing braces around initializer
kenkoh.c:17: warning: (near initialization for ‘data[0]’)

#include <stdio.h>


int main()
{
    int data[4][3] =
    {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9},
        {10, 11, 12}
    };

    size_t obj_size = sizeof(int);
    size_t obj_cnt = sizeof(data)/sizeof(int);
    char *filename = "output.dat";
    FILE *p_file;

    p_file = fopen(filename, "w"); // add a 'b' if using Windoze
    if(p_file != NULL)
    {
        fwrite(&data, obj_size, obj_cnt, p_file);
        fclose(p_file);
    }
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    unsigned int ui;
    unsigned int uj;
    int data[4][3] =
    {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9},
        {10, 11, 12}
    };

    size_t obj_size = sizeof(int);
    size_t obj_cnt = sizeof(data)/sizeof(int);
    char *filename = "output.dat";
    FILE *p_file;

    p_file = fopen(filename, "w"); // add a 'b' if using Windoze
    if(p_file != NULL)
    {
        fwrite(&data, obj_size, obj_cnt, p_file);
        fclose(p_file);
    }

    memset(data, 0, sizeof( data ));

    p_file = fopen(filename, "r"); // add a 'b' if using Windoze
    if(p_file != NULL)
    {
        fread(&data, obj_size, obj_cnt, p_file);
        fclose(p_file);
        for(ui = 0; ui < obj_size; ui++)
        {
            for(uj = 0; uj < obj_cnt/obj_size; uj++)
            {
                printf( "%d ", data[ui][uj] );
            }
        }
        printf( "\n" );
    }

    return 0;
}