C# DWORD and QWORD - signed and unsigned madness

Question

I've noticed that DWord and QWord values when written to the Registry supposed to be Signed Integers, not Unsigned. This code will throw an exception if value is UInt64 or UInt32:

registryKey.SetValue(name, value);

According to MSDN DWORD is a 32-bit unsigned integer (range: 0 through 4294967295 decimal) https://msdn.microsoft.com/en-us/library/cc230318.aspx

So, to write new DWORD value to the Registry I need to cast it to signed integer like so:

UInt32 unsignedValue = (UInt32)someValue;
Int32 signedValue = (Int32)unsignedValue;
registryKey.SetValue(name, signedValue);

Passing unsigned value to SetValue method will throw an exception. Am I missing something or I just being retarded?

Answer 1

For historical reasons, the .NET API/libraries is normally "signed" instead of being "signed + unsigned".

But in the end, a signed int and a unsigned int both occupy the same memory space, and there is no special handling done for negative values. So you can do as you said: cast the unsigned value to signed, write it with SetValue and then if you look at the value in Regedit you'll see that it was written "unsigned".

Note that if your program is compiled in "checked" mode, a more correct code would be:

uint unsignedValue = ... // Your original value

int signedValue = unchecked((int)unsignedValue);
registryKey.SetValue(name, signedValue);

Because in "checked" mode casting between int and uint can throw an exception if the conversion isn't possible.

Note that as written here:

This overload of SetValue stores 64-bit integers as strings (RegistryValueKind.String). To store 64-bit numbers as RegistryValueKind.QWord values, use the SetValue(String, Object, RegistryValueKind) overload that specifies RegistryValueKind.

Clearly you'll have to do the same handling for signed-unsigned.

Answer 2

From the RegistryKey.SetValue page' example:

// Numeric values that cannot be interpreted as DWord (int) values
// are stored as strings.

It seems the stored values are signed ints or strings.