Question

I need to write the content of an array into a file. Let’s suppose I generate random numbers and put them into an array. How do I copy those values into the output file?

[... previous code/declarations ...]

file = open(filename, O_WRONLY|O_CREAT|O_TRUNC, S_IRWXU|S_IWGRP|S_IWOTH);
buffer = (double *) calloc(d, sizeof(double));
for (i = 0; i < d; i++)
{
    double div = (double) (RAND_MAX/0.333);
    double r = rand()/div;
    (*(buffer+i)) = r;
}
write(file, buffer, sizeof(double));

[ ... ]

If I try to read the files, all I see is this memory garbage, nonsense chars all over my screen. Can anyone please help me figuring out what is I do wrong?

Answer 1

The write call is used to write memory blocks to a file, which will seem like garbage mostly if you try to just output the file later. That’s because they will most likely be an IEEE754 binary representation.

If you want a textual representation of the numbers, use something like:

fh = fopen (filename, "w");
for (i = 0; i < d; i++)
    fprintf (fh, "%f\n", buffer[i]);
fclose (fh);