Add rcutils_string_array_sort function

[cottsay]

This change adds a simple and safe mechanism to order the entries in a string_array object lexicographically.

• Linux
• Linux-aarch64
• macOS
• Windows

[Blast545]

I think the strdup part is important and should be addressed

[Karsten1987]

I know, I am late to the party here, but would it make sense to extract the actual sort function qsort into its own function and expose the appropriate API to it? Why I am saying this, is because we have quite a handful of different arrays which could technically all profit from such a sorting function. All the individual arrays had to provide then would be a compare function.

[cottsay]

...extract the actual sort function qsort into its own function and expose the appropriate API to it

Thanks for your interest, @Karsten1987. Could you elaborate on what that might look like? Are you looking for a re-implementation of qsort, or an adapter to make it easier to use with the rcutils arrays?

[Karsten1987]

no, no, please don't reimplement qsort ;-)

What I was trying to say is that if you look at the interface to qsort you'll notice that it's dealing with void *, meaning it's agnostic to its data type. So we could extract that same interface in its own function within rcutils, such as rcutils_qsort or similar, which deals with error checking in a way we'd like it, but basically only wraps qsort.

With that, all different array types could be used simply by providing a tailored compare function. That way, all we can reuse the same sort function for all types:

ret_t rcutils_qsort(string_array, string_array.size, sizeof(char *), &compare_string_array);
ret_t rcutils_qsort(uint8_array,  uint8_array.size, sizeof(uint8_t), &compare_uint8_array)
...

does this make sense?

[cottsay]

Alright @Karsten1987, I took a stab at this, but because of the argument checking, it doesn't come out as clean as I'd like it to. Please have a look and let me know if you see a better way.

[Karsten1987]

I like it quite a bit. I think that makes it really valuable also for other array types 👍

[cottsay]

This PR has changed quite a bit. Resetting reviews...

Lots of changes since review

[Karsten1987]

two little nits. Looks good to me.

[cottsay]

Keen eye, @Karsten1987. I addressed your feedback in f93dc6a. Thanks for reviewing.