Never use the "P" type for the return value unless you are sure the return value will always be '\0'-terminated string (and not what Microsoft calls "Unicode"). If it might be NULL or might be some other type of data, then you have to use the "N" type for the return value.

If the value returned is 0, then you got a NULL. If not, and you are sure it is a pointer to a '\0'-terminated string, then you can use: my $string= unpack "p", pack "L", $ret; to get the string.

Update: While everything I said above is good advice, none of it applies to this problem. ): I read the arguments to Win32::API->new() in the wrong order. "P" is being used for the first argument, not the return value.

The only reason I can think that this might "core dump" is if you have the argument list types wrong or that you pass in a numeric 0 for the ID (and the function doesn't expect a NULL). Perhaps you could post the interface spec for the routine you are calling (since it appears to be a custom DLL, perhaps you could even post the code for that routine).