From: "Berger, Daniel" <Daniel.Berger@...>
Date: 2006-05-15T23:36:36+09:00
Subject: Re: Oddity with Win32API, RegQueryValueEx

> -----Original Message-----
> From: Park Heesob [mailto:phasis68@hotmail.com] 
> Sent: Monday, May 15, 2006 4:31 AM
> To: ruby-talk ML
> Subject: Re: Oddity with Win32API, RegQueryValueEx
> 
> 
> 
> Hi,
> 
> >From: Daniel Berger <djberg96@gmail.com>
> >Reply-To: ruby-talk@ruby-lang.org
> >To: ruby-talk@ruby-lang.org (ruby-talk ML)
> >Subject: Oddity with Win32API, RegQueryValueEx
> >Date: Mon, 15 May 2006 18:45:19 +0900
> >
> >Hi all,
> >
> >Ruby 1.8.4
> >Windows XP
> >
> >I noticed something curious when using the RegQueryValueEx() 
> function 
> >using
> >straight C versus a Win32API wrapper.  Whenever I call it 
> via Win32API, it 
> >always returns ERROR_MORE_DATA (i.e. value 234) on the first 
> call, not 
> >matter what I set the buffer size to.
> >
> >Here's a sample C program that works fine:
> >
> >#include <windows.h>
> >#include <stdio.h>
> >
> >int main(){
> >    char* key =
> >"SYSTEM\\CurrentControlSet\\Services\\EventLog\\Application\\
> SNDSrvc";
> >    char* val = "EventMessageFile";
> >    char buf[1024];
> >    DWORD size;
> >    int rv;
> >    HKEY hk;
> >
> >    rv = RegOpenKeyEx(
> >       HKEY_LOCAL_MACHINE,
> >       key,
> >       0,
> >       KEY_READ,
> >       &hk
> >    );
> >
> >    if(rv == ERROR_SUCCESS){
> >       rv = RegQueryValueEx(hk, val, NULL, NULL, buf, &size);
> >       if(rv == ERROR_SUCCESS){
> >          printf("Success!\n");
> >          printf("Size: %i\n", size);
> >          printf("Buf: %s\n", buf);
> >          RegCloseKey(hk);
> >       }
> >       else{
> >          printf("Failure: %i\n", GetLastError());
> >       }
> >    }
> >
> >    return 0;
> >}
> >
> >However, the equivalent Ruby program always returns ERROR_MORE_DATA:
> >
> >require 'Win32API'
> >
> >HKEY_LOCAL_MACHINE = 0x80000002
> >KEY_READ =  0x20019
> >
> >RegCloseKey = Win32API.new('advapi32', 'RegCloseKey', 'L', 'L') 
> >RegOpenKeyEx = Win32API.new('advapi32', 'RegOpenKeyEx', 
> 'LPLLP', 'L') 
> >RegQueryValueEx = Win32API.new('advapi32', 
> 'RegQueryValueEx', 'LPLPPP',
> >'L')
> >
> >val = 'EventMessageFile'
> >key = 
> >"SYSTEM\\CurrentControlSet\\Services\\EventLog\\Application\\SNDSrvc"
> >hk = [0].pack('L')
> >
> >if RegOpenKeyEx.call(HKEY_LOCAL_MACHINE, key, 0, KEY_READ, hk) == 0
> >    hk   = hk.unpack('L').first
> >    buf  = 0.chr * 1024
> >    size = 0.chr * 4
> 
> should be
>       size = [buf.length].pack('L')

Ah, ok.  I thought it would just set the size regardless.

Thanks,

Dan


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