Re: dynamic variables inside While loop - C# Discussion Boards

11-Mar-08 8:03

Forgive my dull C# questions, but I am a sometimes programmer needing to get up to speed very quickly:
1) Want to dynamically rename a variable within the loop, as in
AltChunkpart#

would become

altChunkpart1
altChunkpart2
etc.

2) Similarly, but it seems to be a special URI-specific case to be part of this line:

Uri uri# = new Uri("/programDescription#.txt", UriKind.Relative);

Uri uri#

would become

Uri uri1
Uri uri2
etc.

Failing to increment the 'uri' within the loop produces this error: "A local variable named 'uri' cannot be declared in this scope because it would give a different meaning to 'uri', which is already used in a 'parent or current' scope to denote something else"

Any guidance will be sincerely appreciated.

Jogannon

Christian Graus11-Mar-08 8:16

Christian Graus

11-Mar-08 8:16

1 - can't be done. Instead, make an array and put that ending digit as the index into the array
2 - can't be done.

Your overall issue is that you have something like this:

Uri uri

for(whateveR)
{
Uri uri;

}

The second Uri can't have the same name as one in the higher scope. Just use a different name, it doesn't need to be different on each iteration, it just needs to be different than the name of the variable it would otherwise hide. Or, just use the same one, if the value does not matter in the higher scope.

string s = "one";

for(whateveR)
{
s = "two";

}

// now s == "two"

Member 278914211-Mar-08 8:29

11-Mar-08 8:29

Thanks Christian. Great explanation. Now let me go and try to apply it.

Jogannon

Member 278914211-Mar-08 9:01

11-Mar-08 9:01

Christian,
I am sorry to be so thick, however I understand the underlying need to have unique variable names. It is a matter of how does s == "two"? I do not see any counting or incrementing code in your example. My own approach (which fails) is to try and append (or concatenate an incrementing int value to the string name. Should I avoid this approach and go with a string array technique instead. Any concrete example will really help at this point.

Thanks,

Jogannon

Christian Graus11-Mar-08 9:10

Christian Graus

11-Mar-08 9:10

"one" and "two" were arbitrary examples - the point was simply that the value given to the variable inside the second scope, applied to the first scope, too. I was illustrating that in your instance, you have a variable named uri in the outer scope, and so you couldn't create one with the same name in the inner scope, and if you reused the outer scope one to keep the same name, you would find that setting it, changed it for the outer scope.

Wow, now I'm confused Smile | :)

I was showing that if you used uri where you were putting Uri uri and getting the error, you would have flow on effects.

If you need to keep the variables you wanted to name uri1, uri2, etc for any reason, a list or array is the way to do that. If you were creating a variable for loop processing that is not reused, then just use a different name, like uriLoop or something.

Member 278914211-Mar-08 9:12

11-Mar-08 9:12

Thanks again, Christian. Let me go and work on this.

Jogannon

Indicate column sorting in DataGridView column

buchstaben11-Mar-08 8:18

buchstaben

11-Mar-08 8:18

Member 2789142 wrote:
it seems to be a special URI-specific case to be part of this line

no, its not uri specific. you try to declare the variable named "uri" multiple times, which is not allowed in this case.

int myInt = 0;

foreach (object obj in objList)
{
  int myInt = 4; // a variable named "myInt" already exists at this time. ovveride the outer variable or use different name
  //..
}

AndrusM11-Mar-08 7:58

AndrusM

11-Mar-08 7:58

I need to indicate that WinForms DataGridView column in sorted.
If column width is too small, sort glyph is not displayed.
Is it possible to force sorth glyph to display in narrow columns also or any other idea how to indicate that column is sorted?

I tried also to underline column caption in mouseclick event but this fails also.

I tried

foreach (DataGridViewColumn dataGridViewColumn in grid.Columns) {<br />
  DataGridViewCellStyle dgvcellStyle = new DataGridViewCellStyle();<br />
  System.Drawing.Font font = new System.Drawing.Font( <br />
dataGridViewColumn.HeaderCell.Style.Font,<br />
            System.Drawing.FontStyle.Underline );<br />
  dgvcellStyle.Font = font;<br />
  dataGridViewColumn.HeaderCell.Style = dgvcellStyle;<br />
  }

But got exception probably since debugger shows that

dataGridViewColumn.HeaderCell.Style.Font

is null.

dataGridViewColumn.HeaderCell.Style is not null.

How to fix ?

Andrus

Help on LINQ

belzer11-Mar-08 7:50

belzer

11-Mar-08 7:50

Hello Forum

I am now getting familiar with LINQ and in need of some help,

I have I Products table with 20 columns but I want to query only 2 columns, the simple way of querying the data

List<Product> ItemList = (from items in dataContext.Products
select items).ToList();

The issue I have is with this example, I am getting back much more data that I really need which is creates extra network traffic etc.

How can I crate a list that will implement only 2 columns of the Product class and the LINQ statement will look something like this

List<Product> ItemList = (from items in dataContext.Products
select new { items.Item_Code, items.Item_Name }).ToList();

[Cross Post] Re: Help on LINQ

Scott Dorman11-Mar-08 8:03

11-Mar-08 8:03

Please don't cross post in multiple forums. It generally won't help you get an answer any quicker. The original post is here[^].

Scott.

—In just two days, tomorrow will be yesterday.
—Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai

Re: [Cross Post] Re: Help on LINQ

belzer11-Mar-08 8:08

belzer

11-Mar-08 8:08

Correct,

I placed the first post not in the correct forum

Re: [Cross Post] Re: Help on LINQ

Scott Dorman11-Mar-08 8:24

11-Mar-08 8:24

belzer wrote:
I placed the first post not in the correct forum

No problem. It is OK to delete a post in this situation, unless there are replies to it. In any case, if you realized it wasn't in the correct forum a link pointing to the correctly placed question is always useful.

Scott.

—In just two days, tomorrow will be yesterday.
—Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai

Re: Help on LINQ

Scott Dorman11-Mar-08 8:50

11-Mar-08 8:50

So is this LINQ to SQL or objects? It sounds like dataContext.Products is a custom object in your data access layer. Have you tried to compile your second example? You may need to do something like this:

var ItemList = (from items in dataContext.Products
select new { items.Item_Code, items.Item_Name });
foreach(var x in ItemList)
{
    Console.WriteLine("{0} - {1} ", x.Item_Code, x.Item_Name);
}

Scott.

—In just two days, tomorrow will be yesterday.
—Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai

Re: Help on LINQ

belzer11-Mar-08 9:17

belzer

11-Mar-08 9:17

What i ended up doing is the following

var ItemList = (from items in dataContext.Products
select new { items.Item_Code, items.Item_Name }).ToList();

thanks.

Re: Help on LINQ

Scott Dorman11-Mar-08 9:40

11-Mar-08 9:40

Sounds like that is working for you then...this looks like what I suggested in my last reply (minus the foreach loop, which was there simply as testing).

Scott.

—In just two days, tomorrow will be yesterday.
—Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai

convert byte[] to short[]

eyalbi00711-Mar-08 7:44

eyalbi007

11-Mar-08 7:44

Hi all,

I need to perfome simple-looking task in C#: Converting byte array to short array - meaning that if my byte array has 100 cells, my short array will have 50 cells.

If it was C/C++ it was simple, using pointers. However in C# I just can't do it - I've already tried using 'unsafe' block and memory pinning using GCHandle, with no success.

Another thing that bothers me in the solutions I found is that the conversion is done using memory copying, which is not necessary, since all the information is already there!

I'll be grateful for any solution!

Thanks,

Eyal.

m@u11-Mar-08 7:54

m@u

11-Mar-08 7:54

this might work

private void foo()
{
	byte[] b = new byte[100];
	IntPtr hnd = Marshal.AllocHGlobal(Marshal.SizeOf(b));
	Marshal.Copy(b,0,hnd,b.Length);
	short[] s = new short[50];
	Marshal.Copy(hnd,s,0,s.Length);
	Marshal.FreeHGlobal(hnd);
}

eyalbi00711-Mar-08 8:01

eyalbi007

11-Mar-08 8:01

Hi,

When using the code you suggested I get the following error:

Type 'System.Byte[]' cannot be marshaled as an unmanaged structure; no meaningful size or offset can be computed.

Eyal.

m@u11-Mar-08 8:08

m@u

11-Mar-08 8:08

oops.. sorry.. use b.Length instead of Marshal.SizeOf(b) Smile | :)

that should do the trick

eyalbi00711-Mar-08 21:48

eyalbi007

11-Mar-08 21:48

Hi,

just wanted to say thanks - this works! the only problem I still have with this solution is that what it does is copying the entire byte[] memory to another location in the memory - what appears to be redundant, since it's already there! in C/C++ all I had to do is one pointer manipulation - can't I do it here as well? is it because the existance of garbage collector?

Thanks!

Eyal.