Why can´t i do this? (C-Code doubt)

Hello,

If i have as a S-Function parameter:

variable1 (with value 0)

And i have an input (u) and an output (y). I want to do this:

double variable3 = 0,*var,*input,*last;

input = &u[0]; /* u[0] is the Simulink block input */

last = &variable1;
var = &variable3;

*var = *input - *last;

if (variable3 > 0){

y[0] = *input; /* y[0] is the Simulink block output */
*last = *input;  ---> This line doesn´t work!, Why?
}

else 

y[0]=0;

I´m trying to implement this code in a S-Function.

Thanks!

[Jan]

What does "doesn'twork" mean? Do you get a warning from the compiler? If so, which one?

[Enrique]

I don´t get any error or warning. The problem is the variable *last, it doesn´t get the value of *input.

[Friedrich]

Are you sure you get in the if branch? maybe add some ssPrintf statements to get some runtime debugging outputs.

Answer 1

[Jan]

Is u a const variable, while last is not?

[Enrique]

How can i change the data type of last?

I try to do:

double * const last;

But i have this error:

error C2166: l-value specifies const object

In the line:

last = &variable1;

Thanks!

[Jan]

Nope, than the const qualifier is most likely not the problem.

How do you check, that *last is not assigned correctly? I'm convinced that the line does assign the value. Therefore I assume, that you expect the changes on the wrong place.

[Enrique]

I see the values creating an another output and this output linked to a "To Workspace" block.

The variable *last always is 0.

Thanks!