I'm getting a crash on the last line of the following Win32::API Call to a National Instruments driver DLL.

# Working Equivalent in C
#    uInt32        data=0x00000000;
#    int32        written;
#DAQmxWriteDigitalU32(taskHandle,1,1,10.0,0,&data,&written,NULL)

#int32 __CFUNC     DAQmxWriteDigitalU32           (TaskHandle taskHand
+le, int32 numSampsPerChan, bool32 autoStart, float64 timeout, bool32 
+dataLayout, const uInt32 writeArray[], int32 *sampsPerChanWritten, bo
+ol32 *reserved);

my $functionDAQmxWriteDigitalU32 = Win32::API->new('nicaiu','DAQmxWrit
+eDigitalU32','IIIFIPPP','I','_cdecl');

my $numSamps = 1;  #int32
my $autoStart = 1;  #bool32
my $timeout = 10.0;   #float64
my $GroupByChannel = 0; #bool32
my $writearray = pack ('N4',0,0,0,0);
my $sampsPerChanWritten= pack("N4",0,0,0,0);
my $reserved = 0;    # NULL *
$return = $functionDAQmxWriteDigitalU32->Call($outTaskHandle,$numSamps
+,$autoStart,$timeout,$GroupByChannel,$writearray,$sampsPerChanWritten
+,$reserved);

[download]

Previous function calls using the outTaskHandle are working fine, I'm pretty sure the problem is in the $writearray parameter (which I need to set to some hex value like 0xF7), the $sampsPerChanWritten which is modified by the C function, or the $reserved pointer which is supposed to be NULL. I've tried many different assignments to $writearray and $sampsPerChanWritten with no luck.

I'm new to Perl, Win32::API and perlmonks so I apologize for formatting issues.

In reply to Win32::API pointers / NULL by ghardy

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