Re: Exception variable never used - C# Discussion Boards

Exception variable never used

7-Jun-04 11:27

Simple: write an application that uses a timer, read-ins the Excel spreadsheet using an interop library (add a reference to Microsoft Excel to your project), and POST the data (see the HttpWebRequest and HttpWebResponse classes) to your ASP.NET application.

If you want help with something specific, then ask about something specific. This forum is intended to help you with programming question, not really to help you design an application.

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Dominik Reichl7-Jun-04 10:03

Dominik Reichl

7-Jun-04 10:03

Hi!

I have a try-catch-finally block, the catch declares some Exception e, but I don't need this e... Now if I compile this I get an unreferenced variable warning...

How to avoid this, unreferenced variable warnings?

Best regards and thanks in advance,
Dominik

_outp(0x64, 0xAD);
and
__asm mov al, 0xAD __asm out 0x64, al
do the same... but what do they do??
(doesn't work on NT)

Dave Kreskowiak7-Jun-04 10:15

7-Jun-04 10:15

try
{
   ... some code that might fail...
}
catch
{
   ... code for handling ALL exceptions ...
}

Note: There is nothing after the catch statement! No unreferenced variables...

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

leppie7-Jun-04 10:42

leppie

7-Jun-04 10:42

Dave Kreskowiak wrote:
try{ ... some code that might fail...}catch{ ... code for handling ALL exceptions ...}

AFAIK an empty catch catches nothing! But to answer the original q.

try { } catch (Exception) { } //look ma, no variables :)

^{top secret xacc-ide 0.0.1}

Heath Stewart7-Jun-04 11:25

7-Jun-04 11:25

True, but that's pretty pointless in reference to what Dave wrote. This type of declaration works best when you want to catch specific exceptions (besides the base Exception class), whether or not you declare an exception variable (I know you know that, leppie, I'm just explaining it to the poster if he manages to read it).

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Dave Kreskowiak7-Jun-04 11:57

7-Jun-04 11:57

Actually, it will catch the Exception. Try it...

try
{
    System.IO.Directory.SetCurrentDirectory(@"Z:\testme");
}
catch
{
    MessageBox.Show(@"Exception caught!");
}

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Using variable in Values for SQL insert

leppie7-Jun-04 12:54

leppie

7-Jun-04 12:54

I think I know why I thought that.

Was running a console app, and waiting for some output in the VS.NET Output console. Eek! | :eek:

~leppie()

^{top secret xacc-ide 0.0.1}

kv_ajay7-Jun-04 8:40

kv_ajay

7-Jun-04 8:40

Hi All,

Just a simple question. I am trying to add the data in a access database (file residing on local machine.) I saw the format and worked according to it. Here is the code.

Console.WriteLine(CBoxCatagory.SelectedItem.ToString());
String sSql = "INSERT INTO MainCatagory" + "(MainCatagory)" + "VALUES("+CBoxCatagory.SelectedText+")" ;
conn.ConnectionString = @"Provider=Microsoft.Jet.OLEDB.4.0;" +@"Data source= C:\" + @"My Documents\db1.mdb";
conn.Open();
OleDbCommand objCommandMain = new OleDbCommand(sSql,conn);
objCommandMain.ExecuteNonQuery();

When I use the fixed or hard data in Values then statement executes fine. But when I am trying to execute with a variable of type ComboBox then it is giving me error. I also tried to use a simple string variable and see the result and it was same. Seems like there is problem in the syntax for adding values using variables.

Here is the error.
An unhandled exception of type 'System.Data.OleDb.OleDbException' occurred in system.data.dll

Can you suggest me something on this one.

Thanks,
Smile | :)

Alvaro Mendez7-Jun-04 8:55

Alvaro Mendez

7-Jun-04 8:55

OK, the first thing I notice is that you're doing a lot of unnecessary string concatenation. The second thing I see is that your CBoxCatagory.SelectedText value is not surrounded in quotes, for the sake of SQL. Try this:

tring sSql = "INSERT INTO MainCatagory (MainCatagory) VALUES('" + CBoxCatagory.SelectedText + "')";<br />
conn.ConnectionString = @"Provider=Microsoft.Jet.OLEDB.4.0;Data source=C:\My Documents\db1.mdb";<br />
...

Regards,
Alvaro

Give a man a fish, he owes you one fish. Teach a man to fish, you give up your monopoly on fisheries.

Anonymous7-Jun-04 9:47

Anonymous

7-Jun-04 9:47

I tried that but it did not work. Then I replaced CBoxCatagory.SelectedText with fix text as Onemore.
It worked fine.
One more thing i observed with my database is that Table Maincatagory has 2 colums. One is maincatagory and other AutoIncrement. When I try to execute the statement with CBox it fails but it increses the AutoIncrement count.
Now does this mean that script is failing in database at insert point bcoz data coming in has wrong format. But I think the format is text so it should not fail anyways.
Any suggestions.

Dave Kreskowiak7-Jun-04 9:55

7-Jun-04 9:55

The SelectedText property of a ComboBox is the selected text in the editable portion of the box. In some cases, SelectedText can return null, especially if your ComboBox is setup with its DropDownStyle set to ComboBoxStyle.DropDownList. Use SelectedItem.ToString() instead.

This could have been easier to diagnose had you been using parameterized queries instead of string concantenations...

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Anonymous7-Jun-04 10:06

Anonymous

7-Jun-04 10:06

I tried that too!
In Fact, I also tried something like this.
String firstString = "ABCCD";
and then used this firstString Var in place of ComboBox var.

Thanks,

Dave Kreskowiak7-Jun-04 10:13

7-Jun-04 10:13

Like I said... Parameterized queries would have fixed this problem from day 1. Using the parameterized version, you don't have to worry about how the strings are escaped in the SQL statement and if there are any special characters in the string that you pass that will screw up the statement syntax. All of that is handled for you, automatically!
There is no reason to NOT use them!

Everything we told you will work under normal circumstances. There is something else you're not telling us, that may seem like a small detail that doesn't mean anything, but makes one hell of a difference to SQL.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Anonymous7-Jun-04 10:36

Anonymous

7-Jun-04 10:36

Though I am kind of new to C# and I exactly dont know the syntax to use parameterized queries, I will try to learn that. Meanwhile, After your stress on nothing wrong in suggestions, I tried to use the same statement in Form Load method and to my surprise it worked. Then I copied same exact statement into Button_Click function (where I was trying previosuly ) and it worked too.
I dont get C# for this. I was always using rebuild for project before attempting any try.

Can you explain this.

Heath Stewart7-Jun-04 11:23

ReadFileEx OVERLAPPED LocalAlloc wows

7-Jun-04 11:23

Look at the documentation for the OleDbCommand.Parameters property. It explains it quite well and gives you examples. Using parameterized queries is highly recommended in ADO.NET because it checks for common security holes and eliminates the need to escape single and double quotes. It's also the only way to import binary data, like when using SqlDbType.Image.

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gdwinslow7-Jun-04 8:03

gdwinslow

7-Jun-04 8:03

Stupid Question:

Scenario:
Need to passé Reference data to my IO engine. It opens-Sends-Closes or it Opens-Listens and sends data to User in call back when data is received, then closes. A pointer that can't be global would be perfect, but C# so ref to data would have to suffice. The ref has all the data to run the engine it self. The IOClass has the engine witch intern uses and API wrapper class for win32 IO functions.

Conundrum:
How do I get the managed ref to go through the win32 IO call back so the IO state engine will work?

Note – the Data object must be pointer for win32 and must be able to be read after the IO is complete by the managed C# code. There have been many articles on the IO functions in question, but now one has solved this as far as I have seen.

Class Guy Winslow
{
public:
WINcontrols
H: 925-606-1091
M: 925-922-0222
gdwinslow@wincontrols.com
};

Heath Stewart7-Jun-04 11:19

7-Jun-04 11:19

It's a little difficult to follow your post, but I'll try...

You're saying the callback function exist in win32 then P/Invoke the callback, create a delegate of the property type in managed code, and create the delegate that points to the P/Invoke call. If you already have a delegate and the P/Invoke'd method and the delegate signatures don't quite match up (may you need to do some custom marshaling, although this case is best solved with an ICustomMarshaler implementation), then define a method which has the right signature and calls the P/Invoke'd win32 callback function.

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gdwinslow7-Jun-04 16:23

gdwinslow

7-Jun-04 16:23

I think i understand what you are talking about. And I thing I am doing this. Sari for mi ignorance new to .NET. This structure my explain better:

[StructLayout(LayoutKind.Sequential)]
public unsafe struct OVERLAPPED
{
public int Internal;
public int InternalHigh;
public int offset;
public int OffsetHigh;
public int hEvent;
public Socket *socket;
}

It’s defined in my API Interface class. This needs to be LocalAlloc, and passed to the ReadFileEx function. This works fine without the Socket pointer, witch is or should be a “ref Socket” to a managed class in C#. I can’t seam to passé it into the OVERLAPPED Structure so the File IO callback can use it to get rest of data and set error info. This socket class instance is created by responses to messages it receives, vary much like Window Sockets. Except it’s our device and not network device. Note - callback must be static. So am I not understanding how you are suggesting to use the P/Invoke or is there something else you guys can suggest.

Class Guy Winslow
{
public:
WINcontrols
H: 925-606-1091
M: 925-922-0222
gdwinslow@wincontrols.com
};

Heath Stewart8-Jun-04 2:55

8-Jun-04 2:55

The Socket class wouldn't work even if it wasn't pinned - it doesn't have a representation in unmanaged code. Instead, you typically declare handles as IntPtrs, and use the Marshal class methods to help with marshaling values. You rarely ever need an unsafe context, either.

In this case, however, you must pin the Socket in memory. There is a chance that the garbage collector (GC) will move the object in managed memory while the unmanaged code is using it. Unmanaged code is just that - unmanaged - so it can't track such changes. Pinning the object in memory will also give you the IntPtr you need. Try something like this, for example:

[StructLayout(LayoutKind.Sequential)]
// The name doesn't matter, so go with .NET naming conventions
public struct OverlappedSocket : IDisposable
{
  public OverlappedSocket(long internal, long internalHigh, int offset,
    int offsetHigh, Socket socket)
  {
    this.Internal = new IntPtr(internal);
    this.InternalHigh = new IntPtr(internalHigh);
    this.Offset = offset;
    this.OffsetHigh = offsetHigh;
 
    // Pin the Socket in memory.
    hEvent = GCHandle.Alloc(socket, GCHandleType.Pinned);
  }
 
  // A ULONG_PTR is processor-dependent - not always 32-bits
  [MarshalAs(UnmanagedType.SysUInt)] public IntPtr Internal;
  [MarshalAs(UnmanagedType.SysUInt)] public IntPtr InternalHigh;
  [MarshalAs(UnmanagedType.U4)] public int Offset;
  [MarshalAs(UnmanagedType.U4)] public int OffsetHigh;
  [MarshalAs(UnmanagedType.SysUInt)] public GCHandle hEvent;
 
  void IDisposable.Dispose()
  {
    // Make sure we free unmanaged resources and let the GC move the Socket
    if (hEvent.IsAllocated) hEvent.Free();
  }
}

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Guy Winslow8-Jun-04 11:17

Guy Winslow

8-Jun-04 11:17

Cool. I was playing with Marshal Attributes last night. That gets me half way there. How do I convert CGHandle back into the Socket class without duplicating it?

unsafe public static void ReadOperation(System.Int32 dwErrorCode, System.Int32 dwNumberOfBytesTransfered, ref CtrlNet_Api.OverlappedSocket lpOverlapped)
{
ref Socket socket = lpOverlapped.hEvent;
}

With my device I am getting chucks of data. So information in the Socket is being changed as Engine runes. When dune or ERRORs out. I set flag in the Socket class for Application to see status, and Trigger and Event for Calling Thread. Tried to get AddrOfPinnedObject but could not find way to cast it as Socket class.

Class Guy Winslow
{
public:
WINcontrols
H: 925-606-1091
M: 925-922-0222
gdwinslow@wincontrols.com
};

Heath Stewart8-Jun-04 11:26

8-Jun-04 11:26

Again, don't use an unsafe context - you don't need it. The best examples of use for unsafe contexts is when it's faster to use pointers to iterate through characters, pixels, etc.

You don't get the Socket from the GCHandle. All the GCHandle does - the way I said to use it - is pin the Socket in memory so unmanaged code doesn't lose a reference to it in case the GC moves it (which it can do). You can still refer to the Socket in managed code just as you are now. Using the IntPtr cast operator or AddrOfPinnedObject method only gets the fixed pointer to the object for use in P/Invoke'd method calls. It doesn't change it as far as managed code is concerned.

Read about the GCHandle structure in the .NET Framework SDK.

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