Error Invalid use of void expression

Question

I have a function int rt_task_start (RT_TASK *task, void(*task_func)(void *arg), void *arg) where in second argument i am passing a function with argument.

Answer 1

I'm not sure how the code in (1) can possibly compile. But here is what you should be using:

int rt_task_start (RT_TASK *task, void(*task_func)(void *arg), void *arg);
int val = 1;
rt_task_start(&demo_task1, demo, &val);

You cannot pass the function pointer bound to a specific argument, that is something like a closure, which isn't available in C. You can, however, pass the function pointer and then separately pass the argument you want to apply (which is what the function signature suggests you should do). But you must pass that argument as a pointer, not a literal.