On Thu, Dec 02, 2021 at 11:29:17PM +0000, Chris Katko via Digitalmars-d-learn wrote: [...]
> It seems I can (thanks to the amazing work of D community) simply do:
> 
> ```d
> extern(C) int sched_yield(void);  // #include <sched.h>
> ```
> 
> however, how does the linker know I need <sched.h> and not some local library, or SDL library, or SDL2.0 library, etc. Shouldn't I be specifying the library somewhere?

An extern(C) function exists in the global namespace, namely, `sched_yield` will bind at link time to whatever library exports the symbol `sched_yield`.  Most linkers (and linker configurations) will generate an error if there are multiple symbols with the same name defined. (The exception is when a symbol is marked as a "weak" symbol, but that's usually not done except for special purposes.)

This is why good libraries like SDL always prefixes their API functions with `SDL_`, for example.  In order to prevent confusion of SDL functions with a function of the same name from another library.


[...]
> Side side question: The above line fails to compile as-is because it
> has (void) instead of ().
> 
> ```
> source/app.d(226,16): Error: cannot have parameter of type `void`
> ```
> 
> Should that be corrected in the compiler? Shouldn't () and (void) be
> interchangeable as long as you're not doing void*?

In C, `int func()` means `func` can take any number of arguments. That's
why you need to write `int func(void)` to explicitly say there are NO
parameters.

But in D, `int func()` means `func` takes no arguments.  So you never
write `int func(void)`. D's `int func()` == C's `int func(void)`.


T

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