How to fix Keil EFM8 Warning C280: unreferenced local variable

Problem:

You have a C function like

int myfunc(int value) {
  return 0;
}

but you see a Keil compiler warning like

*** WARNING C280 IN LINE 7 OF C:\Users\uli\MyProject\src\main.c: 'value': unreferenced local variable

Solution

'value': unreferenced local variable means that you don’t use that variable value in any way.

In the function shown above, you can see that value is the argument of myfunc but myfunc never actually uses the variable.

Do you think that variable should be used in this function?

You need to check your function for typos - the variable is never used at all. Possibly you are using the wrong variable or your function is missing some part of its logic.

Don’t want to use that variable at all?

Usually you can tell the compiler that you don’t want to use that variable by using

(void)value;

but that will produce an expression with possibly no effect warning.

*** WARNING C275 IN LINE 7 OF C:\Users\uli\MyProject\src\main.c: expression with possibly no effect

You can use this hack to avoid this warning:

r = r; // Avoid unused local variable