Server Help

[Qndre]

If I call kernel functions like "RtlMoveMemory" I get "access violation" error message and my self-written Subspace client gets terminated.

Code: Show/Hide Option Explicit '[..] Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory"_ (Dest As Any, Src As Any, ByVal cb&) '[..] Public Function StringToLong(data As String) As Long Dim output As Long Call CopyMemory(output, ByVal data, 4) StringToLong = output End Function Public Function LongToString(data As Long) As String Dim output As String * 4 Call CopyMemory(output, ByVal data, 4) LongToString = output End Function Public Function StringToInteger(data As String) As Integer Dim output As Integer Call CopyMemory(output, ByVal data, 2) StringToInteger = output End Function Public Function IntegerToString(data As Integer) As String Dim output As String * 2 Call CopyMemory(output, ByVal data, 2) IntegerToString = output End Function

You know where the mistake is?

[Qndre]

Cyclovenom told me to move the ByVal keywords to the output. I'll try it without. Seems to work! Thanks!

[Qndre]

No! No! No! No! No! Doesn't work! It doesn't give an error but correct conversion is impossible with the function. I see it because encryption is initialized with a wrong key (server disconnects then). Since nothing else changed this can be the only source for the mistake.
_
If you copy something with RtlMoveMemory you get back something completely different than given! This kernel function is the source of the error! It sucks! Development is impossible with such a buggy kernel! It can't even convert Longs to Strings and Strings To Longs. If you convert a 4-byte String to a Long (at example "test") and back, it isn't "test" any more but some binary information.

[nintendo64]

I don't know what you are exactly doing but for info.

The MoveMemory function moves a block of memory from one location to another.

VOID MoveMemory (

PVOID Destination, // address of move destination
CONST VOID *Source, // address of block to move
DWORD Length // size, in bytes, of block to move
);


Parameters

Destination

Points to the starting address of the destination of the move.

Source

Points to the starting address of the block of memory to move.

Length

Specifies the size, in bytes, of the block of memory to move.



Return Values

This function has no return value.

Remarks

The source and destination blocks may overlap.

The only use for those functions is to put datatypes that are 4 bytes or 2 bytes in little endian byte order.

Example:

http://www.madsci.org/posts/archives/dec96/843185920.Cs.r.html
In each case, the number being represented by the two 32-bit words is "1".


BIG-ENDIAN BYTE ORDER
---------------------

Most Significant Byte Least Significant Byte
vvvvvvv vvvvvvv
+-------+-------+-------+-------+
|byte 0 |byte 1 |byte 2 |byte 3 | "address"
+-------+-------+-------+-------+
| 0 | 0 | 0 | 1 | "value"
+-------+-------+-------+-------+



LITTLE-ENDIAN BYTE ORDER
---------------------

Least Significant Byte Most Significant Byte
vvvvvvv vvvvvvv
+-------+-------+-------+-------+
|byte 0 |byte 1 |byte 2 |byte 3 | "address"
+-------+-------+-------+-------+
| 1 | 0 | 0 | 0 | "value"
+-------+-------+-------+-------+



-nintendo64

[Mr Ekted]

Qndre, stop playing trial and error with programming. It's clear you don't have a clue about BASIC or how software works or Ekted's "Level One Knowledge". You are like a child playing with a control system at a nuclear power plant.
_________________
4,691 irradiated haggis!

[Qndre]

ByVal means that the value is protected in-memory and cannot be modified, so it can't work if you set the output as a ByVal. You set the ByVal keyword in front of a paremeter variable if you want to prevent the called function from modifying it's contents. Since I set the output as a ByVal, it can't be modified by the kernel so it doesn't work! I won't set any of the parameters for the CopyMemory function as a ByVal, so they aren't protected in-memory from being changed.

[Qndre]

If I permit the kernel function to modify the output, I get an access violation! If I don't permit the kernel function to modify the output, I can never get the correct value in the output! That's typically M$ - it sucks!
_
PS: Don't say that I don't know programming! It's a mistake in the Windows kernel which makes this error occour! And it is a known problem! Quote from another forum, posted by someone else:

[nintendo64]

Let me explain how it works and why ByVal is in the correct place, and the Access Violation.

Well Visual Basic when it uses external functions like this uses as a parameter a Pointer for the strings, because that's the parameter asked for the function in this case.

so for a example, as you can see ByVal needs to protect the value of the pointer so it doesn't get changed along the way. If it gets changed NOT USING BYVAL then it will return an access violation, you are altering the memory address of the string. Sometimes it just won't work.

ByVal should only be located where the strings are, this is to allow the transfer of the bytes between both datatypes.

Private Function LongToString(L As Long) As String
Dim S4 As String
S4 = Space(4)
Call CopyMemoryX(ByVal S4, L, 4)
LongToString = S4
End Function

So you see Qndre use a ByVal where it has to be used. In this case it was the strings. Both LongToString, etc... and LongToString... have the use of ByVal with the string.

I wouldn't say the problem is VB, it's a human mistake, althought VB is indeed a problem most of the times, as any language that is so high level.
If you handle things at the low level, or at least use a high level language that enables you to declare your own pointers, you might have more understanding. Certaintly VB could cause some of the errors, but in the functions you need i don't see why, try what i said.

-nintendo64

[Mine GO BOOM]

Can we keep the cursing to a minimum? Also, General Questions are for Server related questions.

-nintendo64

[nintendo64]

[Qndre]

[Mr Ekted]

ByVal is not a protection mechanism. It is the newb way to say "by value" instead of "by address". In C it is done explicitly, and you can refer to data in any way you want.

int x = 7;
int *px = &x;

Function(x); // puts the value 7 on the stack
Function(&x); // puts the address of x on the stack
Function(*px); // puts the value 7 on the stack (what px is pointing at)
Function(px); // puts the address of x on the stack (also the VALUE of px)
Function(&px); // puts the address of px on the stack

Understand what's happening in memory with your data, and you will understand how to use your language.

L1K (tm)

[Qndre]

[Cyan~Fire]

[CypherJF]

That code awfully looks Visual Basic-ish :/
_________________
Performance is often the art of cheating carefully. - James Gosling

[Cyan~Fire]

Acutally, you're right Cyph, maybe Qndre's switched to a higher level language now.

Anyway, if your functions are named correctly, you're trying to convert an ASCII string to an integer? Like "4800" to 0x12C0? If so, then you don't need to copy memory. If you are actually using VisualBasic now, there are the functions CInt() and CLng() that will convert from a string to an integer and long. The = operator will convert from an integer or long to a string for you.

[nintendo64]

[Qndre]

CInt and CLng, etc. do something completely else. At example if you convert the number 123 to a string you have "123" and not the character 123. You can't use Chr and Asc either because Chr only works for Bytes and not for Longs. But this conversion works, but Sasme crashes my client ATM. Need to debug and fix several errors, the client ist still very buggy.

[Cyan~Fire]

Oh, OK, I think I kind of understand what you're doing right now.

I'm not quite sure how a String is implemented by VB. I somehow think that the String reference will not be the start of the actual ASCII string and you'll be getting a bunch of meaningless data instead. Wouldn't reading into a byte array be better for this purpose?

This would all be so easy in C++...