Question

I’m trying to read a number from a file and set it to a public variable in a different class. The function that is reading the file has a pointer-object instance of that class. I’m facing a weird issue:

The following works:

int dummy;
fscanf(file,"%d",&dummy); // assume the file stores the number 10

globals->var = dummy;

cout << "variable is " << globals->var << endl; // this outputs 10 to console. great!

But I’m going to have a lot of fscanf‘s to do, and I don’t want to create all of these redundant dummy variables. I tried the following:

fscanf(file,"%d",&globals->var);
cout << "variable is " << globals->var << endl; // this outputs 2.9e-321 (aka junk)

Is there a reason that doesn’t work? Do I need to do it like globals->&var, or some variation like that? I tried to wrap it in parentheses like so: &(globals->var), but that didn’t work either. Is there a reason this is not working (without me having to paste many many many lines of code)

Thanks!

Answer 1

As you said in the comment, the type of var is double. Yes, that is the problem. You should use %f for it.

Apart from that, I would give you a piece of advice:

Prefer using C++ stream for I/O work. They’re type-safe. If you use them, you would not face this problem which you faced it with fprintf.

Here is how you should use it:

std::ifstream file("filename.txt");
file >> globals->var; //don't worry about whether var is int, or double!

Cool, isn’t it?