Programming

I think it's just an example. An embedded system often has no OS at all, very few libraries, and do-it-yourself memory management.

Thanks to you all for your comments!
So it is believed that:
(1) there is no actual functional difference between the two methods;
(2) it is needed to pass a pointer-to-pointer to a function only if the original value of the "pointer-to-pointer" parameter is used in the function, or we want to change its value in this function. Otherwise, it only increases the function invoking overhead.
(3) it should be careful when return a local pointer value in a function, because a pointer pointing to stack space(local variables) returned to the invoker points to an invalid space. The pointer returned from a subroutine should point to heap space(like malloc()) or global&static variables.

Is that right ?

Not as you've written them, no. I think that's correct, though pointers always make for awkward language. Quite right, stack variables are only valid until the function returns. You can give stack pointers to functions you're calling however, just like you did inside the main() of your first example, since that function is guaranteed to return before main() does.

That was true a couple of decades ago. Nowadays most embedded systems mobile phones for ex. have an OS, virtual memory mgmt and all the libraries. Although the op may be using one that is bare bones but I doubt that otherwise he would not be using malloc and would most likely be coding in assembly language instead of in C.

Small microprocessors are more popular than ever, just not for powering all-singing all-dancing java smartphones. They're in things like MP3 players, wireless mice, cordless phones, monitors, thousands of different USB devices, microwaves, cars... you get the idea. And yes, they are very barebones, and yes, C is very popular for programming them for the most part. There's been a huge explosion of different architectures, developers are fortunate to not have to learn the assembler for them all.