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rakunativecall

Raku/Perl6: how do you code a NULL with NativeCall

https://docs.perl6.org/language/nativecall

 "As you may have predicted by now, a NULL pointer
 is represented by the type object of the struct type."

https://learn.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regqueryvalueexw

 C++
 LSTATUS RegQueryValueExW(
   HKEY    hKey,
   LPCWSTR lpValueName,
   LPDWORD lpReserved,
   LPDWORD lpType,
   LPBYTE  lpData,
   LPDWORD lpcbData
 );

 lpReserved
 This parameter is reserved and must be NULL.

With "native", how do I satisfy the "NULL" requirement?

constant WCHAR   := uint16;
constant DWORD   := int32;

sub RegQueryValueExW( DWORD, WCHARS, DWORD, DWORD, DWORD is rw, DWORD is rw ) is native("Kernel32.dll") returns DWORD { * };

$RtnCode = RegQueryValueExW( $Handle, $lpValueName, int32, REG_DWORD, $lpData, $lpcbData );

"int32" returns:

Cannot unbox a type object (int32) to int in method
CALL-ME at C:\rakudo\share\perl6\sources \947BDAB9F96E0E5FCCB383124F9
23A6BF6F8D76B (NativeCall) line 587

Many thanks, -T

Solution

  • JJ and Brad on the Perl6 mailing list were correct. For a NULL, just pass it a zero. I had a booboo somewhere else.