I agree the new & is confusing and avoid using it at all.
It doesn't mean you can just replace * with & and everything will work as
before.
The safest way to convert pre-j807 code that will modify content of *data
is continue to use * but
remove the leading > (if there) and read result of cd . eg
pre-j807
'...' cd cmd;nr;XX
now
r=. '...' cd cmd;nr;XX
XX=. _1{::r
or
XX=. _1{:: '...' cd cmd;nr;XX
Hope this help.
On Tue, Mar 24, 2020 at 9:51 AM Scott Locklin <[email protected]>
wrote:
> I haven't called a custom DLL in some time now; since I have more spare
> time, I was noodling around with old code.
>
> Took me a while to notice what was going on; "pass by reference" where you
> send a J array to a DLL to be written to wasn't working the way it had in
> the past. It actually is documented, but I had to read about it in the
> forum (this was
> <
> http://jsoftware.2058.n7.nabble.com/j807-cd-pass-array-arguments-td80898.html#a80909
> >
> helpful) to understand what it meant.
>
> I propose that memu be documented here as well as on the "calling DLLs"
> page
>
> https://code.jsoftware.com/wiki/Guides/DLLs/Memory_Management
>
> Also the use of & vs * in the signature is far from clear to me in the
> calling
> DLL <https://code.jsoftware.com/wiki/Guides/DLLs/Calling_DLLs>s page.
> In the past, if I had a function signature like this, and want variable XX
> to be populated in the dll (and returned to J), everything would be fine:
> (for a C function int MyIntMod (int len, int vec[]) which modifies the
> vector of length len )
>
> cmd=. LIBNAME,' MyIntMod i i *i'
> XX =. nr $ 1-1
> cd cmd;nr;XX
> (etc etc)
>
> Now, it only works if I do the following
>
> cmd=. LIBNAME,' MyIntMod i i &i'
> XX =. memu nr $ 1-1
> cd cmd;nr;XX
>
>
> Is this the correct way for modify a vector passed by reference in a DLL?
> If so, when I read the documentation, it looks like it should work with *i
> as well.
>
> "The * type is a pointer to values. A * can be followed by c w u s i l x f
> d
> or j to indicate the type of values. The DLL can read or write this
> memory. The memory is unaliased.
>
> The & type is same as * except the memory is not unaliased as it is assumed
> to be constant."
> Can someone add a sentence for my (presumably common) dll use case? I was
> able to figure it out, but it took me a bit.
>
> -SL
> ----------------------------------------------------------------------
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>
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