Using API RegQueryValueEx with DllImport to read data from Registry

[shrahul]

Hello,

I'm trying to read registry value using the API functions RegOpenKeyEx and RegQueryValueEx along with DllImport in C#. The results show that code runs fine but I'm not getting the desired data. Its returns 0 instead of the data. I'm including the code that I'm using

//*** declarations in the class *****

public static readonly UIntPtr HkeyLocalMachine = (UIntPtr)0x80000002;

public const string lpSubKey = "HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0";

public const int KEY_QUERY_VALUE = 0x1;
public const int REZ_SZ =0x00000002;

[DllImport("advapi32.dll",EntryPoint="RegOpenKeyEx")]
public static extern int RegOpenKeyEx_DllImport(UIntPtr hKey,string lpSubKey,uint ulOptions,int samDesired,out IntPtr phkResult);

[DllImport("advapi32.dll",EntryPoint="RegQueryValueEx")]
public static extern int RegQueryValueEx_DllImport(IntPtr hKey,string lpValueName,int lpReserved,out uint lpType, IntPtr lpData,out uint lpcbData);

//****** declared on load or click event ****

IntPtr hKeyVal;
uint lpType;
uint lpcbData;
IntPtr q=new IntPtr();

int valueRet=RegOpenKeyEx_DllImport(HkeyLocalMachine,lpSubKey,0,KEY_QUERY_VALUE,out hKeyVal);

valueRet=RegQueryValueEx_DllImport(hKeyVal,"ProcessorNameString",0,out lpType, q,out lpcbData);


Output when viewd using different variables :

lpType= returns 1 which signify a string value
q returns 0 *** this should return data but does not
lpcbData returns 48 signifying size of the data being returned.

The return values of the functions show 0 which means success

Any help or insight on "Why I'm unable to get the data" would be highly appreciated.

Thanks
Rahul Sharma

[mehdi62b]

I can't get why you want to use those API functions while there are some classes for this task

 //using Microsoft.Win32;
RegistryKey rk = Registry.LocalMachine.OpenSubKey
("HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0");
string result=rk.GetValue("ProcessorNameString").ToString();
Console.WriteLine(result);

[shrahul]

Thanks a lot for the suggestion mehdi62b but as I'm working on an E-Learning Project I need to demonstrate reading of registry in C# by calling Win 32 API's using DllImport. My hands are tied in this respect. So any help with tha above code would be grately appreciated.

Thanks,
Rahul

[mehdi62b]

when you need a pointer to a string you should use a StringBuilder object,

   //its Definition
   public static extern int RegQueryValueEx_DllImport(IntPtr hKey,string lpValueName,int lpReserved,out uint lpType,StringBuilder sb,out uint lpcbData);

	  //its size should be 100 for having a sufficent capacity for the buffer
   StringBuilder sb=new StringBuilder(100);
   int valueRet=RegOpenKeyEx_DllImport(HkeyLocalMachine,lpSubKey,0,KEY_QUERY_VALUE,out hKeyVal);
   valueRet=RegQueryValueEx_DllImport(hKeyVal,"ProcessorNameString",0,out lpType,sb,out lpcbData);

[shrahul]

Hi,

This is what is troubling me. If I use a StringBuilder object the value returned by the function is 234 which signifies more data is available. This is the case even if I initialize the StringBuilder with 1000.

Even this doesn't help!!!!

Any other suggestion please.

Regards,
Rahul.

[shrahul]

Was finally able to resolve the issue.
Here is the corrected code.

public static readonly UIntPtr HkeyLocalMachine = (UIntPtr)0x80000002;
public static readonly UIntPtr HKEY_CURRENT_USER = (UIntPtr)0x80000001;

public const string lpSubKey = "HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0";

public const long REG_OPTION_NON_VOLATILE = 0x00000000L;

public const int KEY_QUERY_VALUE = 0x1;
public const int REZ_SZ =0x00000002;
public const int KEY_ALL_ACCESS = 0x3F;

[DllImport("advapi32.dll",EntryPoint="RegOpenKeyEx")]
public static extern int RegOpenKeyEx_DllImport(UIntPtr hKey,string lpSubKey,uint ulOptions,int samDesired,out UIntPtr phkResult);

[DllImport("advapi32.dll",EntryPoint="RegQueryValueEx")]
public static extern int RegQueryValueEx_DllImport(UIntPtr hKey,string lpValueName,int lpReserved,out uint lpType,StringBuilder lpData,ref int lpcbData);

UIntPtr hKeyVal;
int valueRet;
uint lpType;

StringBuilder sb=new StringBuilder(100);
int lpcbData=sb.Capacity;

valueRet=RegOpenKeyEx_DllImport(HkeyLocalMachine,lpSubKey,0,KEY_QUERY_VALUE,out hKeyVal);

valueRet=RegQueryValueEx_DllImport(hKeyVal,"ProcessorNameString",0,out lpType,sb,ref lpcbData);

MessageBox.Show("data type : " + lpType.ToString(),"Value",MessageBoxButtons.OK);

MessageBox.Show("data size : " + lpcbData.ToString(),"Value",MessageBoxButtons.OK);

MessageBox.Show("data : " + sb.ToString(),"Value",MessageBoxButtons.OK);

The last parameter in the ReqQueryValueEx was to be Ref instead of out.