Re: [pure-lang-users] C float

[Albert G. <Dr....@t-...>]

John Cowan wrote:
> Casting away const is always safe: const essentially documents how the callee
> uses the argument or its referent.

Exactly. The most important thing you have to keep in mind is that if a 
C routine returns a const pointer, you're not supposed to modify the 
data in Pure. And if a C routine takes a const pointer as argument, you 
can pass it any pointer from Pure (malloced memory, string, etc.) and be 
confident that the C routine won't modify it. Pure also takes care of 
marshalling Pure strings from/to the system encoding if the 
corresponding C type in the Pure extern declaration is char*. That 
usually does the right thing for const char* arguments and return values 
on the C side.

Where things get a bit messy is when you have to pass *non-const* 
pointers as arguments or get them as results. A non-const pointer 
_argument_ is most likely used to return results; in that case you'll 
usually have to malloc some memory to be passed for that parameter, 
maybe initialize the data as required by the C function and decode the 
results and free the memory after the function returns. A non-const 
pointer _return value_ (which isn't also a non-const parameter, such as 
in strcpy) often indicates data malloced by the C routine which is 
supposed to be freed by the caller (i.e., the Pure program).

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag