Solved

String-Arrays and CopyMemory

Posted on 2002-05-23
8
737 Views
Last Modified: 2010-08-05
Hi.
Please have look at the following snippet.
It inserts a value into an array of integers:

private declare sub copymemory ....

Dim intData() as Integer
Redim intData(4)
intData(0)=1:intData(1)=2:intData(2)=3:intData(3)=4:intData(4)=5
' intData is 1,2,3,4,5


' The important thing:
Redim Preserve intData(5)
CopyMemory intData(3), intData(2), Clng(3*2)
intData(2) = 99

' intData is now 1,2,99,3,4,5

Now the Question:
How can i do the same trick with an array of strings(BSTRING) of fixed or variable length.

Regards, holli
0
Comment
Question by:holli
  • 6
  • 2
8 Comments
 
LVL 17

Expert Comment

by:inthedark
ID: 7030124
If noboby comes up with an answer you could do it this way:

Create your string array and also create a pointer to the string array.  Whenever you refer to the string array you always go through the pointer array.  When you add a new element always add it to the last + 1 element in the string array but move the pointer array in the way you used above.

e.g.

a$(0)="Ark"
P(0)=0
a$(1)="Cath"
P(1)=1

Now insert "Bert"

a$(2)="Bert"
P(1) is moved to P(2)
P(1) = 1
0
 
LVL 17

Expert Comment

by:inthedark
ID: 7030125
So to loop through you array:

For c = 0 to Ubound(p)
  msgbox A$(p(c))
Next c
0
 
LVL 17

Expert Comment

by:inthedark
ID: 7030126
Woops....
a$(2)="Bert"
P(1) is moved to P(2)
P(1) = 2 ' got this pointer wrong

 
0
Courses: Start Training Online With Pros, Today

Brush up on the basics or master the advanced techniques required to earn essential industry certifications, with Courses. Enroll in a course and start learning today. Training topics range from Android App Dev to the Xen Virtualization Platform.

 
LVL 6

Author Comment

by:holli
ID: 7032735
thanks so far.

but this is a bit to less for 200 points. but for the excellent and modern programmer you are, it should be not problem for you to clarify that a bit? how about a working sample along with the neccessary declarations?

holli
0
 
LVL 17

Expert Comment

by:inthedark
ID: 7033433
holli, I don't know that copymemory works top down, if it takes a copy of the source memory first it would be better to write the shift in assembler.

Using machine code you can make some space in the middle of an array with just 2 machine code instructions.  So if you app requires speed copymemory may not be the way to go.  What are you tring to acheive?
0
 
LVL 17

Expert Comment

by:inthedark
ID: 7033469
Move memory would be slow, copy memory would not work.

As I thought see:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/kmarch/hh/kmarch/k109_0w8i.asp

And:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/kmarch/hh/kmarch/k109_0zzm.asp

So the solution is to poke some machine code into a string and the execute it.

From memory the machine code you would need would look like this:


PUSH SI
Move SI, PosOfLastByte
PUSH DI
Move DI, SI
ADD DI, WordLength
Move CX, BytesToCopy
MOVD
REPZ
POP DI
POP SI

MOVD would move the first word from SI to DI, then  decrement SI, DI and CX

REPZ would repeate the last instruction until CX was zero.

You would also have to encapsulate the code in a disable/enable interrupts instructions.  
0
 
LVL 17

Accepted Solution

by:
inthedark earned 200 total points
ID: 7033494
But using MoveMemory:

Private Declare Sub MoveMemory Lib "kernel32" Alias "RtlMoveMemory" _
        (hpvDest As Any, hpvSource As Any, ByVal cbCopy As Long)


Private Sub Command4_Click()

ReDim Pointers(1000) As Long ' start big for speed
ReDim Strings(1000) As String ' start big for speed
Dim Elements As Long
Dim c As Long

Elements = 0 ' to start there are no elements

' put first element in pos 0
InsertElement "Able", 0, Strings(), Pointers(), Elements

' put next element in pos 1
InsertElement "Charlie", 1, Strings(), Pointers(), Elements

' put next element in pos 1
InsertElement "Bert", 1, Strings(), Pointers(), Elements


' Now recall elements
Dim m$
m$ = ""
For c = 0 To Elements - 1
    m$ = m$ + Strings(Pointers(c)) + vbCrLf
Next c

MsgBox m$

End Sub

Sub InsertElement(StringData As String, InsertPoint As Long, Strings() _
    As String, Pointers() As Long, Elements As Long)

Dim BytesToCopy As Long
Dim WordLength As Long

If Elements > UBound(Pointers) Then
    ReDim Preserve Pointers(Elements + 1000)
    ReDim Preserve Strings(Elements + 1000)
End If

If Elements > 0 And InsertPoint < Elements Then
    WordLength = 4
    BytesToCopy = (Elements - InsertPoint) * WordLength
    Call MoveMemory(Pointers(InsertPoint + 1), Pointers(InsertPoint), BytesToCopy)
End If

Strings(Elements) = StringData ' put this on the end
Pointers(InsertPoint) = Elements

Elements = Elements + 1

End Sub

0
 
LVL 6

Author Comment

by:holli
ID: 7046581
inthedark, please draw your attention to the related Question at

http://experts-exchange.com/jsp/qManageQuestion.jsp?ta=visualbasic&qid=20306514.
0

Featured Post

Live: Real-Time Solutions, Start Here

Receive instant 1:1 support from technology experts, using our real-time conversation and whiteboard interface. Your first 5 minutes are always free.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Macro: print each sheet to pdf using ExportAsFixedFormat 11 48
Run code from text file in vb 1 64
Child Form in front 4 46
Formula problem with Excel attachment 6 25
There are many ways to remove duplicate entries in an SQL or Access database. Most make you temporarily insert an ID field, make a temp table and copy data back and forth, and/or are slow. Here is an easy way in VB6 using ADO to remove duplicate row…
Article by: Martin
Here are a few simple, working, games that you can use as-is or as the basis for your own games. Tic-Tac-Toe This is one of the simplest of all games.   The game allows for a choice of who goes first and keeps track of the number of wins for…
As developers, we are not limited to the functions provided by the VBA language. In addition, we can call the functions that are part of the Windows operating system. These functions are part of the Windows API (Application Programming Interface). U…
This lesson covers basic error handling code in Microsoft Excel using VBA. This is the first lesson in a 3-part series that uses code to loop through an Excel spreadsheet in VBA and then fix errors, taking advantage of error handling code. This l…

815 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

14 Experts available now in Live!

Get 1:1 Help Now