CopyMemory API

[christiangibbs]

I have been learning about memory. Slowly it is coming together but I am still have problems. I made a simple app that stores a value in a variable. A loop then starts and in that loop I use Bool to switch back and forth adding 1 to variable and then changing it back by subtract 1. I made it continue to switch so I could find its location in memory. I found it with no problems.

Its location:

Hex 0014E618

Dec 1369624

Just so you can check me if needed here is simple app:

Dim trigger As Boolean
Dim looper As Boolean
Dim counter As Integer
 
 
Private Sub Command1_Click()
Wait 4
trigger = False
looper = False
counter = 9022  'store value
  Do While trigger = False
    If looper = False Then
     counter = counter + 1  ' now is 9023
     Me.Print counter   ' show me
     looper = True
    Else
     counter = counter - 1   ' next value back to original
     Me.Print counter  ' show me
     looper = False
    End If
Wait 5
Form1.Cls
  Loop
End Sub

Now I know the location of this variable in memory. I try to use CopyMemory to change the value like so...

Option Explicit
 
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (dest As Any, source As Any, ByVal bytes As Long)
Dim intValue As Long
 
Private Sub Command1_Click()
 
   Wait 4
   Dim address As Long
   address = 1369624   'decimal form
   intValue = 4444  ' new value
   CopyMemory address, intValue, 4
 
End Sub

I have tried..

CopyMemory byval address, intValue, 4

but all I get is a crash.


Any suggestions would be great! TY^^

[sigid]

The answer is easy. You can't do this - at least not in this way...

VB may, at its sole discretion, move variables around in memory during program execution. You need to get the address of the variable IMMEDIATELY before trying to use it. The VARPTR function works fine for a numeric variable. Modify your code so that ADDRESS is made = VARPTR (varname) immediately before each usage, and see if that works.

And - you use "intValue" as a variable name, but if this is REALLY an INTEGER, then the number of bytes to copy is 2, not 4. Use 4 only if intValue is a LONG (and I do NOT mean a variant of type LONG, I mean a real LONG).

[christiangibbs]

"You need to get the address of the variable IMMEDIATELY before trying to use it."

I have been. I get the location each time. This seems like a tough topic. Anyone care to step in?

I have a location in memory in hex form. I know its value and I know what value I want it to be. Please point me in the right direction.


"Dim intValue As Long"

For the record.. it is Long. Just forgot to chage name. :-)

[davidbishton]

This copies from one variable to another.

Private Sub Command1_Click()
Dim lngMyVariable As Long
Dim lngNewValue As Long
 
lngMyVariable = 12345
Debug.Print lngNewValue    'Outputs 0
 
Call CopyMemory(lngNewValue, lngMyVariable, 4)
Debug.Print lngNewValue    'Outputs 12345
 
End Sub

[christiangibbs]

Now if I could only get that to work with a location in memory!

[sigid]

This is code I use regularly - maybe it will help you out to some extent:
(and as a historical footnote, PEEK and its complement, POKE, used to be intrinsic commands in DOS BASIC - this function merely recreates the PEEK fun ctionality)

'<CSCM>
'---------------------------------------------------------------------
'-- Name:   Peek
'--   By:   <SGD> on 04/19/2006
'-- Desc:   Allows you to examine the contents of memory at any address
'--     for any number of bytes and returns this as a string of bytes.
'---------------------------------------------------------------------
'-- Note:   To return STRING data, use PeekStr instead.
'---------------------------------------------------------------------
'-- Revd:   <SGD> on 04/19/2006
'---------------------------------------------------------------------
'-- Parm:   lngAddr (Long)      = The VARPTR of the variable to read, or memory address
'--         lngBytes (Long)     = The number of bytes to read.
'--             Typically, this value is defined as:
'--                 Byte    = 1
'--                 Boolean = 2     (Booleans are implemented as Integers)
'--                 Integer = 2
'--                 Long    = 4
'--                 Single  = 4
'--                 Currency= 8     '-- Use CVC (return string) * 10,000 to get real value
'--                 Double  = 8     '-- Use CVC (return string) * 10,000 to get real value (CVD does NOT work)
'--                 Date    = 8
'--                 Variant = 16
'---------------------------------------------------------------------
'</CSCM>
Public Function Peek(ByVal lngAddr As Long, _
                     ByVal lngBytes As Long) As String
    Peek = Space$(lngBytes)
    CopyMemory ByVal Peek, ByVal lngAddr, ByVal lngBytes
End Function
 
Public Sub PokeLng(ByVal lngAddr As Long, _
                   ByVal lngValue As Long)
    Call CopyMemory(ByVal lngAddr, lngValue, 4&)
End Sub

[christiangibbs]

I can copy and change variables within my app with no problem. The part I am having a problem with is changing a value that I located in memory. I found this ref but can't get it to work.

When the source or the destination is a memory locationyou should pass a 32-bit address by value, for example:

' Copy the contents of a Long variable to the memory location
' pointed to by the "address" variable
Dim address As Long
...
CopyMemory ByVal address, lngValue, 4

location in memory is &H14E618

current value 9022

During my search I found a program that finds locations of values in memory. Its called artmoney. I used it on my app and changed the value stored at that location. I am sure there is a way to do the same thing using api.