Re: anything to do with pointer to functions maybe?

[Jan-Benedict Glaw <jbglaw@lug-owl.de>]

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On Thu, 2004-12-23 11:24:39 +0100, soraberri <421246@posta.unizar.es>
wrote in message <cqe6ed$ldf$1@sea.gmane.org>:
> Hi all!
> I'm having troubles understanding code:
> 
> what type is __sighandler_t if it is defined this way:?
> typedef void (*__sighandler_t) (int);

We define that any signal handling function doesn't return anything
useful (void, that is), and all these functions get a single argument
(of type int) supplied.

> and then, what does this definition  mean:
>  #define SIG_IGN  ((__sighandler_t) 1)	

Also, we don't want *all* signals to actually be handled. Some are to be
ignored. Since we can only use function pointers (now of type
__sighandler_t), we need to have a special magic value (1 in this case)
that we can use.

However, "1" alone doesn't make a good function pointer, nor is it a
function at all or does accept arguments. To "look" like a function
pointer of correct type, "1" is casted to be of __sighandler_t.

There would have been another approach: we could have written a small
function that does nothing and could be used instead. However, it's
address could change, so it doesn't work well as an API. This is why
instead a distenct value (1) is used instead.

MfG, JBG

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