Re: String.empty v.s. string.null - C# Discussion Boards

Re: String.empty v.s. string.null

George_George19-Jun-08 22:50

George_George

19-Jun-08 22:50

Any comments for my analysis for the same question? Smile | :)

http://www.codeproject.com/script/Forums/View.aspx?fid=1649&msg=2605482[^]

regards,
George

Re: String.empty v.s. string.null

George_George19-Jun-08 22:49

George_George

19-Jun-08 22:49

Thanks Zoltan,

1.

I have tested and get the same result from you. I think for string, since == opeartor is overridden, it compares for content of strings, correct?

2.

And for general Object type comparsion, and for the types derived from Object and is not overridden equality comparison operator, I think the memory address other than the content of instances are compared.

regards,
George

Re: String.empty v.s. string.null

Zoltan Balazs20-Jun-08 1:12

Zoltan Balazs

20-Jun-08 1:12

Yes George correct, it is stated clearly in Msdn at the link I posted:

Two string values are considered equal when one of the following is true:

    * Both values are null.
    * Both values are non-null references to string instances that have identical lengths and identical characters in each character position.

Sometimes it's just better to look up the info.

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Re: String.empty v.s. string.null

George_George20-Jun-08 4:00

George_George

20-Jun-08 4:00

Always great to learn from you, Zoltan!

regards,
George

Re: String.empty v.s. string.null

Rutvik Dave19-Jun-08 9:22

Rutvik Dave

19-Jun-08 9:22

Colin Angus Mackay wrote:
Incorrect. Here is what reflector has to say on the subject:
public static readonly string Empty;

That means there is only one representation ever in memory. It is not copied, it is referenced. That means they will ALL point to the same memory address.

Yes I am agree with you.

string s = ""; will create an object in the memory
string s = String.Empty; will NOT create any object, its just a reference.

I also found this on MSDN :

Framework 3.5

((object)"") == String.Empty :::: False
("") == String.Empty         :::: True

Framework 1.1 & 2.0

((object)"") == String.Empty :::: True
("") == String.Empty         :::: True

Thanks for pointing out the mistake. from now onwards i will use String.Empty to save memory overhead.

Re: String.empty v.s. string.null

George_George19-Jun-08 22:53

George_George

19-Jun-08 22:53

Great Rutvik!

I think all references to String.Empty are pointing to the same memory address, where the static member of Empty locates, right?

regards,
George

Re: String.empty v.s. string.null

George_George19-Jun-08 22:45

George_George

19-Jun-08 22:45

Thanks for your attention, Colin! Smile | :)

1.

What do you mean "It is not copied, it is referenced"? Could you show some pseude code please?

2.

"create two different reference type variables and they have same memory reference" -- sorry I do not agree, here is an example, you create a base type variable (reference type) and a derived type variable (reference type), they are of different types but pointing to the same memory address. Please feel free to correct me if I am wrong. Smile | :)

regards,
George

Re: String.empty v.s. string.null

Colin Angus Mackay20-Jun-08 7:07

Colin Angus Mackay

20-Jun-08 7:07

George_George wrote:
What do you mean "It is not copied, it is referenced"? Could you show some pseude code please?

You have two types of objects. Value types and Reference types. Value types are always copied when you pass them around. Reference types are always passed by reference.

You can think of references in code like the references in academic papers. When you read an academic paper you may come across a reference that reads like this [GoF1994]. When you turn to the end of the paper you will see listed all the references. The reference [GoF1994] may be used several times throughout the paper, but it always points to the same item in the list at the end.

If it was copied all the time you wouldn't have a reference and you would have stuff like this copied throughout the paper [Gang of Four, Effective Design Patterns, 1994, Addison Wesley]. By copying the source paper everywhere the academic paper just got much larger. However, a reference can be used to quickly note what academic paper is being used as the source. The reference points to the full detail somewhere else rather than have the full detail repeated constantly.

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Re: String.empty v.s. string.null

George_George23-Jun-08 23:44

George_George

23-Jun-08 23:44

Thanks Colin!

Your reply is clear.

regards,
George

Re: String.empty v.s. string.null

Colin Angus Mackay20-Jun-08 7:11

Colin Angus Mackay

20-Jun-08 7:11

George_George wrote:
"create two different reference type variables and they have same memory reference"

This comment was not made by me.

George_George wrote:
you create a base type variable (reference type) and a derived type variable (reference type), they are of different types but pointing to the same memory address

You have not said what you are assigning to these reference type variables. If it is one existing object that you are assigning to both objects then yes they will point to the same memory.

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Re: String.empty v.s. string.null

George_George23-Jun-08 23:47

George_George

23-Jun-08 23:47

Thanks Colin!

Your reply is clear. Cool!

regards,
George

Re: String.empty v.s. string.null

User 665819-Jun-08 4:32

User 6658

19-Jun-08 4:32

George_George wrote:
I am doing input parameter checking for a string type, and string value except empty is valid. My function is provided to outer client to call. Sometimes I find to check null is not enough, I also need to check String.Empty.

Apart from your original question, you might also use String.IsNullOrEmpty[^] for this task.

regards

modified 12-Sep-18 21:01pm.

Re: String.empty v.s. string.null

George_George19-Jun-08 22:55

George_George

19-Jun-08 22:55

Thanks Greeeg,

Good to learn from you about the new API! Smile | :)

regards,
George

Change the table cell background color

dayakar_dn19-Jun-08 3:31

dayakar_dn

19-Jun-08 3:31

hi,

I have one table, inside this i have one server td.
Now i want to change the table cell background color dynamically i.e from the codebehind page.
If i am giving like this

First.BgColor = System.Drawing.Color.Green.ToString();

here First is my cell id.

But it is not effecting.

can anybody knows the solution, please let me know

Thanks and Regards
Dayakar D.N

Re: Change the table cell background color

leppie19-Jun-08 3:42

leppie

19-Jun-08 3:42

Try another forum. This is for C#.

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IronScheme - 1.0 alpha 4a out now (29 May 2008)

how can I get a running process start-path?

fateme_developer19-Jun-08 1:59

fateme_developer

19-Jun-08 1:59

how can I get a running process start-path?

Re: how can I get a running process start-path?

Bert delaVega19-Jun-08 2:32

Bert delaVega

19-Jun-08 2:32

In the System.Diagnostics namespace, take a look at Process.MainModule.

Re: how can I get a running process start-path?

Giorgi Dalakishvili19-Jun-08 2:36

Giorgi Dalakishvili

19-Jun-08 2:36

What do you know about the process?
If it is the process that launched your code you can use Application.ExecutablePath
You can also use Process class.
If that doesn't help, then try this: Finding Windows Executable[^]

Giorgi Dalakishvili

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creating word document using c#/ vb/ crystal reports

Puneri19-Jun-08 1:41

Puneri

19-Jun-08 1:41

Hello
I'm working on web application in VS 2005. I need to create well formatted
word document report(word file has tables).
How it should be done?
I simply dont know anything about creating and writing to word document thru c#/vb/ crystal report.
Please someone tell me how to deal with this.

TIA,
Leena

Microsoft Reporting Services and C#

jgrogan19-Jun-08 1:24

jgrogan

19-Jun-08 1:24

Hi All,

I'm trying to build some reporting into an app that I've been working on for a while.
The app has a range of class objects in memory, which I want to use to populate the report. In short, I want to push the data to the report at runtime.

I have designed the report structure (and created the .rdlc file), added a report viewer and bound the viewer to the report. However, I cannot seem to access the objects in the report for assignment.

All net searches return info on binding to database tables, but I've found nothing on binding to class objects.

Any ideas / pointers?

Thanks in advance,
John.

Re: Microsoft Reporting Services and C#

carbon_golem19-Jun-08 2:17

carbon_golem

19-Jun-08 2:17

Open the .rdlc file and you should now have a Data menu item in the VS menu. Click Add New Data Source, select Object and go through the wizard.

Scott P

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Re: Microsoft Reporting Services and C#

jgrogan19-Jun-08 3:33

jgrogan

19-Jun-08 3:33

Hi Scott,
I can do that, but once a class is in my data sources tab, I can't look at the componants and can't attach them to a part of my report.
In addition, a lot of the data items I have are time-series items. I will want to set a date for the report and include only data items up to that date. Is there a way to create a dataset in code and dynamically attach it to the report?
Thanks,
John.

Re: Microsoft Reporting Services and C#

carbon_golem19-Jun-08 4:37

carbon_golem

19-Jun-08 4:37

If you have your report active in a tab, you should have a Report menu item. You have to use that to add sources to the particular report. Then you should have them as choices when you put components down on the report. If you didn't know already, you have to pass data in as a generic list even if there's only one object that you're working with. And be warned that the editor is NOT NICE when it comes to revising the report, I can't tell you how many times I've had to manually edit the rdlc file to fix something that the automation broke.

Scott P

instantiate generic list

henze7519-Jun-08 0:38

henze75

19-Jun-08 0:38

Hi,

I've got this piece of code:

Assembly asm = Assembly.LoadFrom(@"C:\Documents and Settings\someDll.dll");
Type type = asm.GetType(someClass);

How can I instantiate a list for the type found above? something like (doesn't work):

System.Collections.Generic.IList<type> list = new System.Collections.Generic.List<type>();

Thanks in advance

Re: instantiate generic list

N a v a n e e t h19-Jun-08 1:15

N a v a n e e t h

19-Jun-08 1:15

Member 3754905 wrote:
How can I instantiate a list for the type found above? something like (doesn't work):

I am not sure I got your question, are you looking to instantiate the type ? Try Activator.CreateInstance()

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