Question

I have the following function which is being called as the start to a module for a program on an embedded AVR clock. I want to get the value from the clock object which will return a date_time structure and copy it into the space I am allocating from the heap.

void time_set_mode_start(Display *display, volatile Controls *controls,
                         volatile TimeKeeper *clock, void *data) {

    DEBUG_LED_PORT |= _BV(DEBUG_LED);
    data = malloc(sizeof(date_time));
}

What is the best way to get data the value returned from clock->getTime() into the data pointer?

Answer 1

One way is to use memcpy. Specifically, you would probably want memcpy(data, clock->getTime(), sizeof(date_time)).

Another way — probably better, now that I think about it — is to use ordinary assignment:

*((date_time*)data) = *(clock->getTime());

This treats data as a date_time *, and assigns a value to the date_time object that it points to.

(Note: in both of the above code-snippets, I’m assuming that clock->getTime() returns a date_time *. Is that correct?)

By the way, I should point out that data = malloc(sizeof(date_time)); will completely replace the original void * data that was passed in. Your caller will never see the memory location that data now points to, because the pointer is being passed by value.