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program fails to get RegistryKey on particular Win10 box

I have a small subroutine to check for the existence of a required server program, as follows:
private bool IsProgramInstalled(string programDisplayName)
{
string logstr = string.Format("Checking install status of {0}....", programDisplayName);
RegistryKey rk = Registry.LocalMachine.OpenSubKey("SOFTWARE\\Bridge Club Utilities");
foreach (string s in rk.GetSubKeyNames())
{
Console.WriteLine(s);
if (s != null)
{
if (s.Equals(programDisplayName))
{
AppendToLog(logstr + " INSTALLED");
return true;
}
}
}
AppendToLog(logstr + " NOT INSTALLED", Color.Red);
return false;
}
I have installed the program containing the above subroutine on many Windows boxes with no problems, but one customer receives an 'Unhandled Exception' error on program startup, as shown below:
When I loaded VS2022 on the customer's machine and ran it in debug mode, the exception appears on the line that sets RegistryKey rk, as shown below:
So I thought this user had maybe installed the required server program (BridgeComposer) in the wrong place, or the registry was screwed up somehow, or there was a permissions issue. I tried running my app in 'administrative mode', but this did not solve the problem.
Next, I tried to see if the user's PC had the same registry entries as my PC, and it appears that they do. If I manually navigate to 'Computer\HKEY_LOCAL_MACHINE\SOFTWARE\RegisteredApplications' on both machines, I see the same entry for 'BridgeComposer' as shown below:
Clearly I'm doing something wrong/stupid, but I have no clue what it is. Any pointers/clues would be appreciated.

Most likely your program is running as 32-bit on a 64-bit computer and is therefore searching in HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node.
There are a number of ways one can approach this:
Use Registry.OpenBaseKey and specify the desired Registry View.
Compile for AnyCPU, but uncheck Prefer 32-bit (Project => <project name> Properties... => Build => Uncheck Prefer 32-bit)
Compile for 64-bit
Option 1:
Note: The following is untested, but should work - it's a slight modification of the code in your OP.
private bool IsProgramInstalled(string programDisplayName, RegistryView regView = RegistryView.Registry64)
{
string logstr = string.Format("Checking install status of {0}....", programDisplayName);
using (RegistryKey localKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, regView))
{
if (localKey != null)
{
using (RegistryKey rk = localKey.OpenSubKey(#"SOFTWARE\Bridge Club Utilities"))
{
if (rk != null)
{
foreach (string s in rk.GetSubKeyNames())
{
Console.WriteLine(s);
if (s != null)
{
if (s.Equals(programDisplayName))
{
AppendToLog(logstr + " INSTALLED");
return true;
}
}
}
}
}
}
}
AppendToLog(logstr + " NOT INSTALLED", Color.Red);
return false;
}

c# default application - how to get the file content? [duplicate]

I'd like to to associate a file extension to the current executable in C#.
This way when the user clicks on the file afterwards in explorer, it'll run my executable with the given file as the first argument.
Ideally it'd also set the icon for the given file extensions to the icon for my executable.
Thanks all.

There doesn't appear to be a .Net API for directly managing file associations but you can use the Registry classes for reading and writing the keys you need to.
You'll need to create a key under HKEY_CLASSES_ROOT with the name set to your file extension (eg: ".txt"). Set the default value of this key to a unique name for your file type, such as "Acme.TextFile". Then create another key under HKEY_CLASSES_ROOT with the name set to "Acme.TextFile". Add a subkey called "DefaultIcon" and set the default value of the key to the file containing the icon you wish to use for this file type. Add another sibling called "shell". Under the "shell" key, add a key for each action you wish to have available via the Explorer context menu, setting the default value for each key to the path to your executable followed by a space and "%1" to represent the path to the file selected.
For instance, here's a sample registry file to create an association between .txt files and EmEditor:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\.txt]
#="emeditor.txt"
[HKEY_CLASSES_ROOT\emeditor.txt]
#="Text Document"
[HKEY_CLASSES_ROOT\emeditor.txt\DefaultIcon]
#="%SystemRoot%\\SysWow64\\imageres.dll,-102"
[HKEY_CLASSES_ROOT\emeditor.txt\shell]
[HKEY_CLASSES_ROOT\emeditor.txt\shell\open]
[HKEY_CLASSES_ROOT\emeditor.txt\shell\open\command]
#="\"C:\\Program Files\\EmEditor\\EMEDITOR.EXE\" \"%1\""
[HKEY_CLASSES_ROOT\emeditor.txt\shell\print]
[HKEY_CLASSES_ROOT\emeditor.txt\shell\print\command]
#="\"C:\\Program Files\\EmEditor\\EMEDITOR.EXE\" /p \"%1\""

Also, if you decide to go the registry way, keep in mind that current user associations are under HKEY_CURRENT_USER\Software\Classes. It might be better to add your application there instead of local machine classes.
If your program will be run by limited users, you won't be able to modify CLASSES_ROOT anyway.

If you use ClickOnce deployment, this is all handled for you (at least, in VS2008 SP1); simply:
Project Properties
Publish
Options
File Associatons
(add whatever you need)
(note that it must be full-trust, target .NET 3.5, and be set for offline usage)
See also MSDN: How to: Create File Associations For a ClickOnce Application

Here's a complete example:
public class FileAssociation
{
public string Extension { get; set; }
public string ProgId { get; set; }
public string FileTypeDescription { get; set; }
public string ExecutableFilePath { get; set; }
}
public class FileAssociations
{
// needed so that Explorer windows get refreshed after the registry is updated
[System.Runtime.InteropServices.DllImport("Shell32.dll")]
private static extern int SHChangeNotify(int eventId, int flags, IntPtr item1, IntPtr item2);
private const int SHCNE_ASSOCCHANGED = 0x8000000;
private const int SHCNF_FLUSH = 0x1000;
public static void EnsureAssociationsSet()
{
var filePath = Process.GetCurrentProcess().MainModule.FileName;
EnsureAssociationsSet(
new FileAssociation
{
Extension = ".binlog",
ProgId = "MSBuildBinaryLog",
FileTypeDescription = "MSBuild Binary Log",
ExecutableFilePath = filePath
},
new FileAssociation
{
Extension = ".buildlog",
ProgId = "MSBuildStructuredLog",
FileTypeDescription = "MSBuild Structured Log",
ExecutableFilePath = filePath
});
}
public static void EnsureAssociationsSet(params FileAssociation[] associations)
{
bool madeChanges = false;
foreach (var association in associations)
{
madeChanges |= SetAssociation(
association.Extension,
association.ProgId,
association.FileTypeDescription,
association.ExecutableFilePath);
}
if (madeChanges)
{
SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_FLUSH, IntPtr.Zero, IntPtr.Zero);
}
}
public static bool SetAssociation(string extension, string progId, string fileTypeDescription, string applicationFilePath)
{
bool madeChanges = false;
madeChanges |= SetKeyDefaultValue(#"Software\Classes\" + extension, progId);
madeChanges |= SetKeyDefaultValue(#"Software\Classes\" + progId, fileTypeDescription);
madeChanges |= SetKeyDefaultValue($#"Software\Classes\{progId}\shell\open\command", "\"" + applicationFilePath + "\" \"%1\"");
return madeChanges;
}
private static bool SetKeyDefaultValue(string keyPath, string value)
{
using (var key = Registry.CurrentUser.CreateSubKey(keyPath))
{
if (key.GetValue(null) as string != value)
{
key.SetValue(null, value);
return true;
}
}
return false;
}

There may be specific reasons why you choose not to use an install package for your project but an install package is a great place to easily perform application configuration tasks such registering file extensions, adding desktop shortcuts, etc.
Here's how to create file extension association using the built-in Visual Studio Install tools:
Within your existing C# solution, add a new project and select project type as Other Project Types -> Setup and Deployment -> Setup Project (or try the Setup Wizard)
Configure your installer (plenty of existing docs for this if you need help)
Right-click the setup project in the Solution explorer, select View -> File Types, and then add the extension that you want to register along with the program to run it.
This method has the added benefit of cleaning up after itself if a user runs the uninstall for your application.

To be specific about the "Windows Registry" way:
I create keys under HKEY_CURRENT_USER\Software\Classes (like Ishmaeel said)
and follow the instruction answered by X-Cubed.
The sample code looks like:
private void Create_abc_FileAssociation()
{
/***********************************/
/**** Key1: Create ".abc" entry ****/
/***********************************/
Microsoft.Win32.RegistryKey key1 = Microsoft.Win32.Registry.CurrentUser.OpenSubKey("Software", true);
key1.CreateSubKey("Classes");
key1 = key1.OpenSubKey("Classes", true);
key1.CreateSubKey(".abc");
key1 = key1.OpenSubKey(".abc", true);
key1.SetValue("", "DemoKeyValue"); // Set default key value
key1.Close();
/*******************************************************/
/**** Key2: Create "DemoKeyValue\DefaultIcon" entry ****/
/*******************************************************/
Microsoft.Win32.RegistryKey key2 = Microsoft.Win32.Registry.CurrentUser.OpenSubKey("Software", true);
key2.CreateSubKey("Classes");
key2 = key2.OpenSubKey("Classes", true);
key2.CreateSubKey("DemoKeyValue");
key2 = key2.OpenSubKey("DemoKeyValue", true);
key2.CreateSubKey("DefaultIcon");
key2 = key2.OpenSubKey("DefaultIcon", true);
key2.SetValue("", "\"" + "(The icon path you desire)" + "\""); // Set default key value
key2.Close();
/**************************************************************/
/**** Key3: Create "DemoKeyValue\shell\open\command" entry ****/
/**************************************************************/
Microsoft.Win32.RegistryKey key3 = Microsoft.Win32.Registry.CurrentUser.OpenSubKey("Software", true);
key3.CreateSubKey("Classes");
key3 = key3.OpenSubKey("Classes", true);
key3.CreateSubKey("DemoKeyValue");
key3 = key3.OpenSubKey("DemoKeyValue", true);
key3.CreateSubKey("shell");
key3 = key3.OpenSubKey("shell", true);
key3.CreateSubKey("open");
key3 = key3.OpenSubKey("open", true);
key3.CreateSubKey("command");
key3 = key3.OpenSubKey("command", true);
key3.SetValue("", "\"" + "(The application path you desire)" + "\"" + " \"%1\""); // Set default key value
key3.Close();
}
Just show you guys a quick demo, very easy to understand. You could modify those key values and everything is good to go.

The code below is a function the should work, it adds the required values in the windows registry. Usually i run SelfCreateAssociation(".abc") in my executable. (form constructor or onload or onshown) It will update the registy entry for the current user, everytime the executable is executed. (good for debugging, if you have some changes).
If you need detailed information about the registry keys involved check out this MSDN link.
https://msdn.microsoft.com/en-us/library/windows/desktop/dd758090(v=vs.85).aspx
To get more information about the general ClassesRoot registry key. See this MSDN article.
https://msdn.microsoft.com/en-us/library/windows/desktop/ms724475(v=vs.85).aspx
public enum KeyHiveSmall
{
ClassesRoot,
CurrentUser,
LocalMachine,
}
/// <summary>
/// Create an associaten for a file extension in the windows registry
/// CreateAssociation(#"vendor.application",".tmf","Tool file",#"C:\Windows\SYSWOW64\notepad.exe",#"%SystemRoot%\SYSWOW64\notepad.exe,0");
/// </summary>
/// <param name="ProgID">e.g. vendor.application</param>
/// <param name="extension">e.g. .tmf</param>
/// <param name="description">e.g. Tool file</param>
/// <param name="application">e.g. #"C:\Windows\SYSWOW64\notepad.exe"</param>
/// <param name="icon">#"%SystemRoot%\SYSWOW64\notepad.exe,0"</param>
/// <param name="hive">e.g. The user-specific settings have priority over the computer settings. KeyHive.LocalMachine need admin rights</param>
public static void CreateAssociation(string ProgID, string extension, string description, string application, string icon, KeyHiveSmall hive = KeyHiveSmall.CurrentUser)
{
RegistryKey selectedKey = null;
switch (hive)
{
case KeyHiveSmall.ClassesRoot:
Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(extension).SetValue("", ProgID);
selectedKey = Microsoft.Win32.Registry.ClassesRoot.CreateSubKey(ProgID);
break;
case KeyHiveSmall.CurrentUser:
Microsoft.Win32.Registry.CurrentUser.CreateSubKey(#"Software\Classes\" + extension).SetValue("", ProgID);
selectedKey = Microsoft.Win32.Registry.CurrentUser.CreateSubKey(#"Software\Classes\" + ProgID);
break;
case KeyHiveSmall.LocalMachine:
Microsoft.Win32.Registry.LocalMachine.CreateSubKey(#"Software\Classes\" + extension).SetValue("", ProgID);
selectedKey = Microsoft.Win32.Registry.LocalMachine.CreateSubKey(#"Software\Classes\" + ProgID);
break;
}
if (selectedKey != null)
{
if (description != null)
{
selectedKey.SetValue("", description);
}
if (icon != null)
{
selectedKey.CreateSubKey("DefaultIcon").SetValue("", icon, RegistryValueKind.ExpandString);
selectedKey.CreateSubKey(#"Shell\Open").SetValue("icon", icon, RegistryValueKind.ExpandString);
}
if (application != null)
{
selectedKey.CreateSubKey(#"Shell\Open\command").SetValue("", "\"" + application + "\"" + " \"%1\"", RegistryValueKind.ExpandString);
}
}
selectedKey.Flush();
selectedKey.Close();
}
/// <summary>
/// Creates a association for current running executable
/// </summary>
/// <param name="extension">e.g. .tmf</param>
/// <param name="hive">e.g. KeyHive.LocalMachine need admin rights</param>
/// <param name="description">e.g. Tool file. Displayed in explorer</param>
public static void SelfCreateAssociation(string extension, KeyHiveSmall hive = KeyHiveSmall.CurrentUser, string description = "")
{
string ProgID = System.Reflection.Assembly.GetExecutingAssembly().EntryPoint.DeclaringType.FullName;
string FileLocation = System.Reflection.Assembly.GetExecutingAssembly().Location;
CreateAssociation(ProgID, extension, description, FileLocation, FileLocation + ",0", hive);
}

The file associations are defined in the registry under HKEY_CLASSES_ROOT.
There's a VB.NET example here that I'm you can port easily to C#.

There are two cmd tools that have been around since Windows 7 which make it very easy to create simple file associations. They are assoc and ftype. Here's a basic explanation of each command.
Assoc - associates a file extension (like '.txt') with a "file type."
FType - defines an executable to run when the user opens a given "file type."
Note that these are cmd tools and not executable files (exe). This means that they can only be run in a cmd window, or by using ShellExecute with "cmd /c assoc." You can learn more about them at the links or by typing "assoc /?" and "ftype /?" at a cmd prompt.
So to associate an application with a .bob extension, you could open a cmd window (WindowKey+R, type cmd, press enter) and run the following:
assoc .bob=BobFile
ftype BobFile=c:\temp\BobView.exe "%1"
This is much simpler than messing with the registry and it is more likely to work in future windows version.
Wrapping it up, here is a C# function to create a file association:
public static int setFileAssociation(string[] extensions, string fileType, string openCommandString) {
int v = execute("cmd", "/c ftype " + fileType + "=" + openCommandString);
foreach (string ext in extensions) {
v = execute("cmd", "/c assoc " + ext + "=" + fileType);
if (v != 0) return v;
}
return v;
}
public static int execute(string exeFilename, string arguments) {
ProcessStartInfo startInfo = new ProcessStartInfo();
startInfo.CreateNoWindow = false;
startInfo.UseShellExecute = true;
startInfo.FileName = exeFilename;
startInfo.WindowStyle = ProcessWindowStyle.Hidden;
startInfo.Arguments = arguments;
try {
using (Process exeProcess = Process.Start(startInfo)) {
exeProcess.WaitForExit();
return exeProcess.ExitCode;
}
} catch {
return 1;
}
}

How to find all after effect installed version in c#?

I have problem for detecting the all after effects installed version in c# i used this code for getting the name
static string[] GetAllInstalledSoftware(string strPrefix)
{
const string strUNINSTALL_KEY = #"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall";
List<string> listMatches = new List<string>();
// Enumerate all sub keys found under the "Uninstall" key, each sub key represents a installed software
foreach (string strSubKey in Registry.LocalMachine.OpenSubKey(strUNINSTALL_KEY).GetSubKeyNames())
{
// try to get the "DisplayName" for the installed software
object objValue = Registry.LocalMachine.OpenSubKey(strUNINSTALL_KEY + #"\" + strSubKey).GetValue("DisplayName");
if (objValue != null)
{
string strDisplayName = objValue.ToString();
// If display name starts with the desired prefix
if (strDisplayName.StartsWith(strPrefix))
{
// -> add it to the result list
listMatches.Add(strDisplayName);
}
}
}
return listMatches.ToArray();
}
But it only give me only one latest installed name for after effect but i have installed 3 version of after effects CS5, CS6, CC-2014,
so anybody have solution how to find all installed version of after effects?

Outlook 2k7 Integration (via P/Invoke) - Blocking unsafe attachments

We're currently developing a plug-in for a piece of software in C#. This plug-in extracts the contents of a PST file and stores all items in it as text files (with the exception of attachments, which are stored as their type in the same folder as the email).
It has been working without issue until we tested it on Windows 7 w/ Outlook 2K7. After running the same previous job on a machine with Outlook 2000 on it, we noticed that there were over 12,000 files missing. These files turned out to be attachments (mostly URLs)
We found that the issue is that Outlook 2K7 blocks attachments with specific extensions. If you open the email in Outlook itself, you see a blue bar at the top stating "Outlook blocked access to the following potentially unsafe attachments" and all the attachments in the emails.
Is there a way to programmatically get these attachments without Outlook blocking them?
The code we use to save the attachments is:
private void saveAttachment(ref object oEmail, StoreInfo currentStoreInfo, string sEmailID, string sExportPath)
{
int iAttachCount = 0;
object oAttach = null;
oAttach = getNextAttachment(oEmail, ref iAttachCount);
while (oAttach != null)
{
saveAttachment(sEmailID, sExportPath, oAttach);
oAttach = getNextAttachment(oEmail, ref iAttachCount);
}
}
private object getNextAttachment(object oEmail, ref int iAttachCount)
{
object oAttach = null;
try
{
iAttachCount++;
oAttach = GetProperty(oEmail, "Attachments", new object[] { iAttachCount });
}
catch //(Exception ex)
{
// There was no attachment to be gotten
oAttach = null;
}
return oAttach;
}

Just putting this on here in case anybody else runs into the same issue. Outlook 2K7 has a Level1 file type feature that blocks access to attachments with specific extensions.
However, you can change the registry to allow access to these files. Just remember to set it back to the way it was prior to you modifying it for security's sake.
private void SetLevel1RemoveValues()
{
// Get the base key for the current user HKEY_CURRENT_USER
Microsoft.Win32.RegistryKey regKey = Microsoft.Win32.RegistryKey.OpenRemoteBaseKey(Microsoft.Win32.RegistryHive.CurrentUser, "");
// Get the security key from the registry
Microsoft.Win32.RegistryKey subKey = regKey.OpenSubKey("Software\\Microsoft\\Office\\" + sCurrentOutlookVersion + ".0\\Outlook\\Security", true);
// If the Outlook\Security key doesn't exit, create one
if (subKey == null)
subKey = regKey.CreateSubKey("Software\\Microsoft\\Office\\" + sCurrentOutlookVersion + ".0\\Outlook\\Security");
// Loop through each Value in the registry to see if the Level1Remove key already exists.
string[] sValues = subKey.GetValueNames();
bool bHasLevel1RemoveKey = false;
foreach (string sValue in sValues)
if (sValue == "Level1Remove")
bHasLevel1RemoveKey = true;
// If the key already exists, store the data so we can reset it later
if (bHasLevel1RemoveKey)
sPrevLevel1RemoveValues = subKey.GetValue("Level1Remove").ToString();
else
sPrevLevel1RemoveValues = "";
// Create an array of all Level 1 Extensions
string[] level1Extensions = new string[] { ".ade", ".adp", ".app", ".asp", ".bas", ".bat",
".cer", ".chm", ".cmd", ".com", ".cpl", ".crt", ".csh", ".exe", ".fxp", ".gadget",
".hlp", ".hta", ".inf", ".ins", ".isp", ".its", ".js", ".jse", ".ksh", ".lnk",
".mad", ".maf", ".mag", ".mam", ".maq", ".mar", ".mas", ".mat", ".mau", ".mav", ".maw",
".mda", ".mdb", ".mde", ".mdt", ".mdw", ".mdz", ".msc", ".msi", ".msp", ".mst", ".ops",
".pcd", ".pif", ".pfr", ".prg", ".pst", ".reg", ".scf", ".scr", ".sct", ".shb", ".shs",
".tmp", ".url", ".vb", ".vbe", ".vbs", ".vsmacros", ".vss", ".vst", ".vsw",
".ws", ".wsc", ".wsf", ".wsh" };
// Set the value in the registry to the list of all Level 1 extensions so we can extract them
subKey.SetValue("Level1Remove", string.Join(";", level1Extensions));
// Close (and save) the values
subKey.Close();
regKey.Close();
}

Getting location of file tnsnames.ora by code

How can I get the location of the tnsnames.ora file by code, in a machine with the Oracle client installed?
Is there a windows registry key indicating the location of this file?

Some years ago I had the same problem.
Back then I had to support Oracle 9 and 10 so the code only takes care of those versions, but maybe it saves you from some research.
The idea is to:
search the registry to determine the oracle client version
try to find the ORACLE_HOME
finally get the tnsnames from HOME
public enum OracleVersion
{
Oracle9,
Oracle10,
Oracle0
};
private OracleVersion GetOracleVersion()
{
RegistryKey rgkLM = Registry.LocalMachine;
RegistryKey rgkAllHome = rgkLM.OpenSubKey(#"SOFTWARE\ORACLE\ALL_HOMES");
/*
* 10g Installationen don't have an ALL_HOMES key
* Try to find HOME at SOFTWARE\ORACLE\
* 10g homes start with KEY_
*/
string[] okeys = rgkLM.OpenSubKey(#"SOFTWARE\ORACLE").GetSubKeyNames();
foreach (string okey in okeys)
{
if (okey.StartsWith("KEY_"))
return OracleVersion.Oracle10;
}
if (rgkAllHome != null)
{
string strLastHome = "";
object objLastHome = rgkAllHome.GetValue("LAST_HOME");
strLastHome = objLastHome.ToString();
RegistryKey rgkActualHome = Registry.LocalMachine.OpenSubKey(#"SOFTWARE\ORACLE\HOME" + strLastHome);
string strOraHome = "";
object objOraHome = rgkActualHome.GetValue("ORACLE_HOME");
string strOracleHome = strOraHome = objOraHome.ToString();
return OracleVersion.Oracle9;
}
return OracleVersion.Oracle0;
}
private string GetOracleHome()
{
RegistryKey rgkLM = Registry.LocalMachine;
RegistryKey rgkAllHome = rgkLM.OpenSubKey(#"SOFTWARE\ORACLE\ALL_HOMES");
OracleVersion ov = this.GetOracleVersion();
switch(ov)
{
case OracleVersion.Oracle10:
{
string[] okeys = rgkLM.OpenSubKey(#"SOFTWARE\ORACLE").GetSubKeyNames();
foreach (string okey in okeys)
{
if (okey.StartsWith("KEY_"))
{
return rgkLM.OpenSubKey(#"SOFTWARE\ORACLE\" + okey).GetValue("ORACLE_HOME") as string;
}
}
throw new Exception("No Oracle Home found");
}
case OracleVersion.Oracle9:
{
string strLastHome = "";
object objLastHome = rgkAllHome.GetValue("LAST_HOME");
strLastHome = objLastHome.ToString();
RegistryKey rgkActualHome = Registry.LocalMachine.OpenSubKey(#"SOFTWARE\ORACLE\HOME" + strLastHome);
string strOraHome = "";
object objOraHome = rgkActualHome.GetValue("ORACLE_HOME");
string strOracleHome = strOraHome = objOraHome.ToString();
return strOraHome;
}
default:
{
throw new Exception("No supported Oracle Installation found");
}
}
}
public string GetTNSNAMESORAFilePath()
{
string strOracleHome = GetOracleHome();
if (strOracleHome != "")
{
string strTNSNAMESORAFilePath = strOracleHome + #"\NETWORK\ADMIN\TNSNAMES.ORA";
if (File.Exists(strTNSNAMESORAFilePath))
{
return strTNSNAMESORAFilePath;
}
else
{
strTNSNAMESORAFilePath = strOracleHome + #"\NET80\ADMIN\TNSNAMES.ORA";
if (File.Exists(strTNSNAMESORAFilePath))
{
return strTNSNAMESORAFilePath;
}
else
{
throw new SystemException("Could not find tnsnames.ora");
}
}
}
else
{
throw new SystemException("Could not determine ORAHOME");
}
}

On Windows, the most likely locations are either %ORACLE_HOME%/network/admin or %TNS_ADMIN% (or the TNS_ADMIN registry setting). These two cover almost every installation.
Of course it is possible to have a working Oracle client without this file. Oracle has bewildering array of networking options, and there are plenty of ways to achieve a working setup with using TNSNAMES. Depending on what you are trying to achieve here, your first port of call might be the sqlnet.ora file, which is also found in %ORACLE_HOME%/network/admin. This should contain a line that looks something like this:
NAMES.DIRECTORY_PATH= (LDAP, TNSNAMES, HOSTNAME)
TNSNAMES means it will use the TNSNAMES.ora file (second in this case). LDAP and HOSTNAME are alternate ways of resolving the database. If there is no TNSNAMES the TNSNAMES.ora file will be ignored if it exists in the right place.
In C# / .NET this should get you the environment variables:
Environment.GetEnvironmentVariable("ORACLE_HOME");
Environment.GetEnvironmentVariable("TNS_ADMIN");

List<string> logicalDrives = Directory.GetLogicalDrives().ToList();
List<string> result = new List<string>();
foreach (string drive in logicalDrives)
{
Console.WriteLine("Searching " + drive);
DriveInfo di = new DriveInfo(drive);
if(di.IsReady)
result = Directory.GetFiles(drive, "tnsnames.ora", SearchOption.AllDirectories).ToList();
if (0 < result.Count) return;
}
foreach (string file in result) { Console.WriteLine(result); }

According to the net that depends on the version of Oracle and the working directory of the SQL*Plus process. This first link tells you the environment variable that specifies the base path for some versions (7, 8, 9i) of Oracle. If you use a different one, I'm sure there's a similar way to get to the system directory.
If you spread versions of these files all over the place though and rely on the "look for a local tnsnames.ora first" behaviour of the client, then I guess you're out of luck.

I'm not a C# or a Windows guy for that matter so hopefully this helps. The tnsnames.ora file should be located in:
ORACLE_HOME\network\admin
If an alternate location has been specified, it should be available via the TNS_ADMIN registry key.
See this link for more information on how Oracle handles tns names on Windows.