Create Registry Value, but only if it doesn't exist

Archive: Create Registry Value, but only if it doesn't exist

grzech
31st July 2006 00:29 UTC

Create Registry Value, but only if it doesn't exist
I want to write a DWORD into Windows Registry, but only if such value doesn't exist already. Unfortunately WriteRegDWORD will overwrite existing value if it exists.

How can I do this?

TIA

Comperio
31st July 2006 04:07 UTC

Try ReadRegDWORD
From the docs:

The error flag will be set and $x will be set to an empty string ("" which is 0) if the DWORD is not present.

So, if the return value from ReadRegDWORD is an empty string ("") and the error flag is set after reading, then you'll know the value does not exist and you can proceed.

grzech
31st July 2006 13:14 UTC

I have read documentation on ReadRegDWORD before, the point is I cannot find anything about "error flag" in the docs.
How do I check if it has been set?

Afrow UK
31st July 2006 14:37 UTC

ClearErrors first, IfErrors after.

-Stu

grzech
31st July 2006 15:04 UTC

Thanks.
So I have made something like this:

Var myvalue
ClearErrors
myvalue = ReadRegDword ...
${If} $myvalue == 0
  IfErrors 0 +3
    WriteRegDWORD ...
    WriteRegDWORD ...
${EndiF}

Is this correct?

Afrow UK
31st July 2006 15:07 UTC

You can do ${If} ${Errors} with LogicLib too.

${If} $myvalue == 0
${AndIf} ${Errors}
WriteRegDWORD ...
WriteRegDWORD ...
${EndIf}

-Stu

grzech
31st July 2006 17:12 UTC

I have problem with declaring variable

I got error: "Invalid command: Var" on line:

Var myvalue

Afrow UK
31st July 2006 17:15 UTC

Unless /GLOBAL is specified, you must use Var outside Sections and Functions.
You might as well just put Var instructions at the top of your script.

-Stu

grzech
31st July 2006 17:39 UTC

Ok, forget it I don't want to use any library.
So back to the drawing board:

ClearErrors
ReadRegDword $0 ...
StrCmp $0 0 0 +4  ;I would like something better here? How to compare DWORD?
IfErrors 0 +3
  WriteRegDWORD ...
  WriteRegDWORD ...

Is that Ok?

grzech
31st July 2006 19:38 UTC

There shoud be:
StrCmp $0 "" 0 +4

instead of:
StrCmp $0 0 0 +4

And it works now.
Thanks Afrow.

Afrow UK
31st July 2006 23:03 UTC

It might be wise to do the IfErrors check before the StrCmp, although it probably won't matter, but it's good practice.

-Stu

grzech
1st August 2006 22:38 UTC

Yes, you're right. I am not very familiar yet with this NSIS syntax so my code is far from being perfect. I'll change it to:


ClearErrors
ReadRegDword $0 ...
IfErrors 0 +4
  StrCmp $0 "" 0 +3 
    WriteRegDWORD ...
    WriteRegDWORD ...