|
Nope. You can pass a value (ByVal) or a reference (ByRef, it boils down to the address of a value); a function/method cannot discover how it got what it got or how it used to be called inside the caller.
So
Dim a as int = 123
Dim b as int = 123
myfunc(a)
myfunc(b)
myfunc(123)
all look the same when looking at the parameter from inside myfunc.
And that is all right for almost all situations. A function should react on its input values, they make the "contract". The one time I regret not being able to get the name is to simplify logging, where one would want to write
log(a)
log(b)
to get the output
a = 123
b = 123
but alas that is not possible.
|
|
|
|
|
Hi Luc
Thanks for your explanation.
This sentence of yours get my attention
Luc Pattyn wrote: You can pass a value (ByVal) or a reference (ByRef, it boils down to the address of a value)
So, If I used Byref, (I am guessing here) The parameter inside the function header should have pointer/link to the calling variable, so later on, the parameter declared by "ByRef" will send the value back to the calling variable.
How the parameter knows which variable?
The real requirement for my question is this:
I am creating a generic function that able to update single field in a table, the function look like this
Update(TableName,FieldName,FieldValue,pkName,pkValue)
calling the function is like this
Update("customers","Address","USA","id",4)
that will update the address field in customer table where id = 4.
What I am trying to do is reducing the number of the parameter in this function to be
Update(TableName,FieldValue,pkValue)
and call it by
Dim address as string = "USA"
Dim id as integer = 4
Update("Customers",address,id)
where address is acting as 2 things
1- the field name inside the table as "address"
2- the field value which need to be updated as "USA"
That was my idea, it seem it will not see the light
|
|
|
|
|
Hi again,
I'm not quite sure what you want.
1.
ByRef should be explained well in the documentation and in your VB book. In essence, assuming
Function myfunc(ByRef x as Integer)
x = x + 1
End Function
will increment the variable in the caller, if it really is a variable
Dim a as integer = 12
myfunc(a)
' now a equals 13
myfunc(a+1)
' calculates a local hidden value of 13, which the function then increments, but noone can access any more
2.
what do you mean by "table"? is it an array? a DataTable? or something else entirely.
You might want to show the declaration (and specify the language: VB6 or VB.NET)
Although the conclusion almost certainly will be: can't be done.
|
|
|
|
|
Hi again.
for No 1, as in your example
How "x" knows that it should return it is new value to "a"?
Is there a link between them?
I mean, maybe I can use this link to get what I want?
(I know the answer is NO but I am just clarifying my question)
I hope it is clear
For No 2, I mean Table name inside Sql Server and I am using vb.net . what is vb6?  (kidding)
Update(TableName as string,FieldName as string,pkname as string, pkvalue as string)
then I build the sql statement
sql = "UPDATE @tablename SET @fieldname = @fieldvalue WHERE @pkname = @pkvalue"
Then I substitute each @variable with the correct parameter
I got your answer very well, I will search for another crazy idea
|
|
|
|
|
Sam Martini wrote: How "x" knows that it should return it is new value to "a"?
it doesn't. By using the ByRef keyword, what gets passed is not the number 12 but the address of something that holds the value 12. If the calling parameter is a simple variable (or an array element), it would be the address of that variable/element, otherwise (i.e. when it is a constant or an expression) the expression gets evaluated, its value stored in a temporary location (say on stack), and the address of that result gets passed. All that is the compiler's job.
|
|
|
|
|
Very informative and useful.
Thank you for your time.
|
|
|
|
|
you're welcome.
|
|
|
|
|
 you want to force the caller of your function to hold the passed value in a special named variable!!! 
ok, maybe you find my comment annoying - but it seems you have to learn some basics about "functions", "parameters", "value types" and "reference types". If you do, such questions or "solutions" will never come to your mind, and it's worth the cost in the long term!
Your problem, if I got it right, is solvable by good old: "another level of indirection"...
|
|
|
|
|
Well, First, I don't know in which category I can put your answer, it is annoying as you said, "Yes", but I will not kill my self if that is your purpose :P
Second, I don't know if you read the whole conversation, that what I am asking for can be done in C, and Foxpro, and Python so, knowing the basics of the function or parameter will not help much. If you work in another programming language such Foxpro or Python, I guess it is normal to check if that can be done in vb.net such as these 3 language above.
Third, I know to overcome what I am asking about and that by using old trick being used since vb6 old days which is the collection or hashtable
Dim par1 As New Hashtable
par1.Add("'USA'","address")
myfunc("customer",par1)
Function myfunc(ByVal TableName As String,FieldNameValue As Hashtable)
Dim sql = "SELECT * from " + TableName + " WHERE " + FieldNameValue.Item(key:=FieldNameValue.Keys(0)) + " = " + FieldNameValue.Keys(0)
MsgBox(sql)
End Function
As I said, I am building my framework, asking for some technique if it exist or no, may change the whole idea of my coding in case the answer was "yes"
Forth, this is personal question to you.
Since old days of vb6 and till 2010 of each release, people asking such question, and we got always the same answer "No", ok, but why? because vb is not a scripting language. arrrg, so? why not include such powerful technique in the vb? that will cause Microsoft to lost money regarding it supported in c? why not vb after 4 .net release does not has it? it should be piece of cake for the developer with the existing of that nasty reflection in there hands. That will help a lot of building dynamic Sql statement and building code on the fly and execute it. Security issue? then remove it from c.
my question here not to Microsoft, but to you.
Why you are against it?
|
|
|
|
|
Thank you for your long reply.
I've read the whole conversation, and I'm aware this things can be done in other languages - in C you would do it with the pre-processor... others mentioned it.
So you want't to do this now with .Net, - This lead me to my "not so nice" answer. I just wanted to mention, there a good reasons not to use pre-processors with "textual replacement" any more. If you are planing your framework, you shouldn't force the callers to know which variable names to use, so I said "learn about parameter passing".
@4: This is not so difficult: "Powerful technique" - is the wrong word for "textual replacement" - this is what you wan't. So personally I'm happy with no pre-processing and textual replacement any more. I was a C/C++ programmer long enough to know about the power of macros, but I never missed the nasty debugging (real compile-time type-checking is not possible for the compiler).
Today I would use a "hashtable/dictionary - workarround" you showed, or generate the code on the fly, or use reflection - but the best you can do - check your requirement and think realy hard if you need this. I'm for sure not the smartest person on the planet - but I'm programming for a living for enough years now to "smell" a bad solution. I wanted to do the same thing in the past, but I resisted, and found a better solution. -Again, please don't be angry about my "learn about basics"-statement.
I hope you find a nice solution for your framework and users!
greetings
![Rose | [Rose]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/rose.gif)
|
|
|
|
|
johannesnestler wrote: check your requirement and think realy hard if you need this
NO I don't need this
I got your answer very clearly.
I am not an expert in .Net, I moved to it having in mind that it had every thing. I mean by every thing that it has collected all the technique in other languages.
I asked many question in msdn forum, most of them the answer was no.
can that be done:
dim x as myclass
x.Find("customers", <-- after this the intellisinse get list of all fields from sql server so I can list them. The answer was NO
Can I have multiple copy of vs2010 where each one start with it is own setting such as syntax color and loading of extension. the answer was NO
Can I list the local variable inside the function/sub i am currently working in, the answer is NO
These question is not for you or any one to answer, i am just telling you that in my mind I had overdose of expectation about .net, now, I will say ".Net is very powerful, but you should know it is limitation" so that i am asking this kind of question.
I hope you did not get bored with my second long answer, and thank you for you second explanation which I got it 100%
Cheers
|
|
|
|
|
some thoughts:
.NET and it's tooling is a programming environment like many others. If you want to use it's power, you have to use it in the right problem domain. .NET has a huge "problem domain" it can be applied to. You can write Web/Desktop/Mobile/Database-Apps with one Framework. You can use different languages, etc.
You shure don't get "every thing" from it, but i think it's very much compared to other frameworks.
What you have to know is the same for every kind of programming - How you solve your problems with it.
As an example - for all the problems you mentioned there maybe is an solution.
* You can implement your own intellisense behavior, but magic is impossible...
* An VisualStudio-AddIn would do - all IDE settings live in one file (you can export them...) - Shure you need for using AddIn...
* The intellisense lists all local variables you have defined... ? If you use the rigth naming conventions you can tell which are the "global" ones.
What I want to say is: Create some projects, look how others solved common programming problems in .Net - and learn from it. If you are smart in solving problems, you will always find your solution. If you wan't to change the IDE to your needs, do it - if you don't like it- make your own. (easier than it sounds!) - .NET clearly gives you the power.
You will always find limitations in a technology - but .NET is so complete,open and clear - you can bend it to your will! 
|
|
|
|
|
Hi again
johannesnestler wrote: * You can implement your own intellisense behavior, but magic is impossible...
That mean, creating my own plug-in VSIX, and use it. And that is not an easy task which I will never do since I can live without it. I prefer wasting my time on something new for my project to the customer that earn me money. I thought such thing can be done in 5 min.
using Enum? Very very very bad idea. so, No answer
johannesnestler wrote: * An VisualStudio-AddIn would do - all IDE settings live in one file (you can export them...)
That work for loading the syntax color and setting the programming language environment, but not for choosing which extension to be loaded where most extensions require to restart VS. Once again I thought that is easy to do by few clicking.
johannesnestler wrote: * The intellisense lists all local variables you have defined... ? If you use the rigth naming conventions you can tell which are the "global" ones
I got the same answer from msdn, that is not an answer more than workaround. Once I get advised not to use naming convention since the .net environment is smart enough to tell where is the error when assigning wrong type to a variable. And now I had to use to solve my simple question which I thought it is (BY DEFAULT) should be there.
I had to change what is in my thoughts
johannesnestler wrote: .NET clearly gives you the power.
I consider the above as an answer to all my questions. .Net gives you the power to any thing, but do it your self. 
Nice talking to you
|
|
|
|
|
Sam Martini wrote: So, If I used Byref, (I am guessing here) The parameter inside the function header should have pointer/link to the calling variable
No, the pointer is not to a variable, but to a memory location. At runtime, variable names don't exist.
|
|
|
|
|
Hello Dave
Dave Kreskowiak wrote: At runtime, variable names don't exist.
Thanks, I got it now. although it still a bit fuzzy of how other language can do it.
"Understanding" is always hard part of being a programmer
|
|
|
|
|
... of how other language can do it:
1. Pre-processor = textual replacement in the code file before(!) compiling
2. Interpreted languages - reading your code...
...
Compiled to native processor instructions: No variable names, or logic depending on it ...
|
|
|
|
|
But if you were a C dinosaur, you could write
#define log(x) fprintf(stderr, "#x = %g\n", x);
Software rusts. Simon Stephenson, ca 1994.
|
|
|
|
|
which I used to do quite a lot.
the C pre-processor was a powerful tool, and at least one CP member is using it even on C# code!
|
|
|
|
|
Luc Pattyn wrote: which I used to do quite a lot.
So did I!
Luc Pattyn wrote: the C pre-processor wasIS a powerful tool
ftfy
Luc Pattyn wrote: at least one CP member is using it even on C# code!
 Where's the :shudder: smiley when you need it?
Software rusts. Simon Stephenson, ca 1994.
|
|
|
|
|
You rang?
It's just a text processor; you can use it with pretty much any text file.
|
|
|
|
|
PIEBALDconsult wrote: It's just a text processor; you can use it with pretty much any text file.
I beg to differ.
IMO it only works rather well for you because C# and C/C++ are sufficiently related syntax-wise. The pre-processor has to understand where it should and shouldn't try and apply define and macro substitutions; it should not modify stuff inside comments and string literals, so it knows about /* and // comments, and it knows "abcd" and "ab\"cd" are untouchable. If (horresco referens) you feed it VB source code, you won't like the outcome.
|
|
|
|
|
Peter_in_2780 wrote: But if you were a C dinosaur
I am C egg dinasaur. 
I know nothing about C, except it is very powerful and very very hard
|
|
|
|
|
|
I guess it is a common question with common answer as well
|
|
|
|
|
I have a Shockwave Flash Object (named webFlash) in my form. I'm trying to use StretchBlt to magnify the object. Ideally I would like to push a button and have it replace the Flash Object on my form with the magnified version.
Any help would be appreciated, even just documentation on how to use StrechBlt because I can't find anything on it. Thank you.
The code below I found browsing the web. It was originally for a mouse cursor, but I'm trying to adapt it.
Private Declare Function GetCursorPos Lib "user32" (ByRef lPointCoordinateoint As PointAPI) As Integer
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lplWindowName As String) As Integer
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Integer, ByVal hWnd2 As Integer, ByVal lpsz1 As String, ByVal lpsz2 As String) As Integer
Private Declare Function GetDC Lib "user32" (ByVal hwnd As Integer) As Integer
Private Declare Function StretchBlt Lib "gdi32" (ByVal hdc As Integer, ByVal X As Integer, ByVal Y As Integer, ByVal nWidth As Integer, ByVal nHeight As Integer, ByVal hSrcDC As Integer, ByVal xSrc As Integer, ByVal ySrc As Integer, ByVal nSrcWidth As Integer, ByVal nSrcHeight As Integer, ByVal dwRop As Integer) As Integer
Private Declare Function GetDesktopWindow Lib "user32" () As Integer
Private Declare Function ReleaseDC Lib "user32" (ByVal hwnd As Integer, ByVal hdc As Integer) As Integer
Private Structure PointAPI
Dim X As Integer
Dim Y As Integer
End Structure
Dim PointCoordinate As PointAPI
Dim lWind As Integer
Dim lDesktop As Integer
Dim lButton As Integer
Private Sub Video_Mag_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Video_Mag.Click
Dim lWind As Object
lWind = GetDesktopWindow()
lDesktop = GetDC(lWind)
lButton = GetDC(Me.Handle.ToInt32)
Timer.Enabled = True
End Sub
Private Sub Timer_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer.Tick
GetCursorPos(PointCoordinate)
' ? > Origin X > Origin Y > Size X > Size Y > ? >
StretchBlt(lButton, _
webFlash.Location.X + webFlash.Width + 1, _
webFlash.Location.Y + webFlash.Height + 1, _
webFlash.Width, _
webFlash.Height, _
lDesktop, _
webFlash.Location.X + webFlash.Width, _
webFlash.Location.Y + webFlash.Height, _
124, 60, &HCC0020)
End Sub
|
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
