Question

Im trying to write and read an array of ints in a binary file. The two functions look like this, more or less.

savefunction

int numbers[6]={0, 2, 3, 3, 0, 1};
FILE *file;
if(file=fopen(filename, "wb")==NULL)
{
    printf("Something went wrong reading %s\n", filename);
    return 0;
}
else
{
    int i;
    for(i=0; i<6; i++)
        fprintf(file, "%d", numbers[i]);
}
fclose(file);

loadfunction

FILE *saved_data;
int errors=0;
if((saved_data=fopen(filename, "rb"))==NULL)
    errors++;
else
{
    fread(first, sizeof(int), 1, saved_data);
    fread(second, sizeof(int), 1, saved_data);
    fread(third, sizeof(int), 1, saved_data);
    fread(fourth, sizeof(int), 1, saved_data);
    fread(fifth, sizeof(int), 1, saved_data);
    fread(sixt, sizeof(int), 1, saved_data);
}
fclose(saved_data);

Now when I debug the program the debugger tells me that the first element is the following

(gdb) print first
$1 = (int *) 0x7fff5fbff968
(gdb) print *first
$2 = 858993200

I can’t understand this. The file when opening with editor says 023301

Answer 1

The complementary function of fread is fwrite, not fprintf. What you’re doing with fprintf is putting the integers into the file as text, not as binary.

Also, make sure you pass a pointer to fread, not an integer. You don’t show the declarations of first, second, and so on, but if you’ve declared something like

int first, second, third, fourth, fifth, sixt;

then you’ll need to use code like

fread(&first, sizeof(int), 1, saved_data);

rather than

fread(first, sizeof(int), 1, saved_data);

Since your integers are already in an array, you can just write the array in one go with

fwrite(numbers, sizeof(int), 6, file);

and avoid the for loop altogether.