Reading strings, integers etc from files using fscanf

Question

I'd like your help with understanding how should I do the following:

I have a file that contains integers separated by spaces ' '. I need to read all integers, sort them and write them as a strings to another file. I wrote a code, but I read char by char, put the word in an char sub_arr [Max_Int] and when I met ' ', I put these chars, now one string, after atoi-ing it into another Main int array,until reaching the end of the file, string by string, and then I sorted and itoa-ing them and wrote them in another file.

But then I remembered that there's a fscanf function:I read about it and still I didn't understand completely what does it do and how to use it.

In my case, where all integers separated by space, can I write fscanf(myFile,"%s",word)? would it know not to consider ' ' and stop at the end of the specific string?! How?

More than that, Can I write fscanf(myFile,"%d",number) and it would give me the next number itself? (I must have misunderstood it. Feels like magic).

Answer 1

You are right, fscanf can give you the next integer. However, you need to provide it with a pointer. Therefore, you need an & behind number:

fscanf(myFile, "%d", &number);

*scanf family of functions also automatically skip whitespace (except when given %c, %[ or %n).

Your loop with reading file will eventually look like this:

while (you_have_space_in_your_array_or_whatever)
{
    int number;
    if (fscanf(myFile, "%d", &number) != 1)
        break;        // file finished or there was an error
    add_to_your_array(number);
}

---

Side note: you may think of writing like this:

while (!feof(myFile))
{
    int number;
    fscanf(myFile, "%d", &number);
    add_to_your_array(number);
}

This, although looks nice, has a problem. If you are indeed reaching the end of file, you will have read a garbage number and added to your data before testing the end of file. That is why you should use the while loop I mentioned first.