Defining []NA call that requires a pointer to a pointer.

[norbertjurkiewicz84]

What's the best way to define this. I have a function that takes 2 arguments, see def. below.

int GetErrorMsg(int ErrorNo, char **errMsg)

I'm sure I can go the route of global alloc but is there a clean way to get this sting back?

[Vince|Dyalog]

Hi Norbert,

On MS Windows and a Dyalog 32-bit Unicode, I think the following will get you what you want.

⎕NA 'I4 thedll.dll|GetErrorMsg <0T P'

errMsg is a double indirect—as you mention, a pointer to a pointer.

To read errMsg, you’ll need to use the MEMCPY and STRNCPY techniques as shown in the ⎕NA documentation.

e.g.
'addrget' ⎕NA 'dyalog32|MEMCPY >P[] P U4'
addrget 1 ppaddr 4 ⍝ Where ppaddr is the char** errMsg from GetErrorMsg

The above gets a pointer to a character string so that we can pass it to STRNCPY:

'strget' ⎕NA 'dyalog32|STRNCPY* >0T1[] P U4'

Regards,

Vince