[SOLVED] Pass result "y" to inline function

[newe12]

Hi!

I have to pass the result "y", which is correctly calculated in a function in mainwindow.cpp, to the inline function in the header file (where "y" is needed):

inline double f(double x)
{
      double y;
      return y+3*x;
}

this function is called in the same function of the mainwindow.cpp-file where "y" is calculated before.

It compiles fine, but "y" is not passed.

How can I tell the programme to pass "y" to be used in the inline function of the header?

I appreciate any useful comments!

[SGaist]

Hi,

That's rather a general C++ question but:

Is y a member of your class ? If not, add it as parameter to f otherwise, remove double y;

On a side note, you should consider using more meaning full names for your functions and variables. Your code will be way easier to read and understand.

[newe12]

Thanks @SGaist ! Solved!

I changed it to:

inline double fun(double x, double constant)
{
return constant+3*x;
}

and it works!

[sosun]

I can't get the point, but I'll try: You want the y to be passed to the fun with its calculated before value? Am I right? If so, you probably want to pass it by reference:

inline double fun(double x, double& constant) {
    return constant+3*x;
}

Also, you should not call variables "constant" until they're constant like const double sum; or whatever with const keyword.

[SGaist]

@sosun, why as a reference ? constant is just used not modified.

But I agree on the naming point. By the way, a constant that is recalculated is not really a constant

[sosun]

@SGaist Aah, I didn't understand the question rightly. You was right.

[newe12]

@SGaist that's true!

"x" is the variable or better "argument" of the function "fun". The constant is basically the result of a variable from a function from within an interval. Nevertheless, it is calculated before "fun" is called and it is simply not changed any more within the function! So I renamed it to "resultbefore" :-).

inline double fun(double x, double resultbefore)
{
return resultbefore+3*x;
}

Anyway, it works! There was a another small problem which I have removed now. Also thanks to @sosun !

[SGaist]

Again, it's not really better. What does that variable represent ? Number of atoms in a quartz crystal ? Number of waves hitting a riff ? That's the kind of thing you should refer to when deciding variable names.