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Posted 23 Sep 2006

# How to write a Memory Scanner using C#

, 23 Sep 2006 CPOL
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Search a process' memory to find specified 16, 32 or 64 bit data values.

## Introduction

Have you ever had a problem completing a game because your health meter shows just 5% of your health available?
Have you ever used a game trainer to solve this problem?
Have you ever wondered how this trainer freezes your health meter to 100%?
These game trainers, do a simple job!
They write a little part of the Game's memory with the 100 `value`!
But how to find the exact part of memory?

## The Question and the Answer

Q: How to find the location in which a program stores a `value` in its memory?
A: Some programs named 'Memory Scanners', are written to read and search a program's memory for exact location and help freezing it! (And I have written this article to show you, how to write a 'Memory Scanner')

## Step 1: Where to begin?

Let's have a look at a program's memory.
Think that I have written a program and we can have a look at its memory.
To have a picture in mind, we can say, it looks something like this:

As you can see, the memory is made up of a huge number of small sectors, that hold a `value` in it. Our picture, just shows a small part of the memory, from sector 0 to sector 99 and a detail of sector 0 to sector 15. But as you know, a computer just knows the meaning of 0 and 1, so what do these Hexadecimal `value`s mean?

Let's take a deep look at the memory again.

As you can see, every byte is made up of 8 bits with each of them being just that 1 or 0, and in Binary mode, they can return the `value` stored in the byte((00010111)2 = (23)10 = (17)16).

As we saw, a computer's memory stores information by holding the 0 and 1s in the memory bits, and 8 bits of memory make a section of memory named byte, so a byte can hold `value`s up to (11111111)2 = (255)10 = (FF)16, but how about the bigger `value`s?
We usually work with `value`s greater than 255!
Ok, the answer is that, we have bigger units of memory to hold the bigger `value`s.

Let's look at another picture of memory that shows the bigger units and then, I will explain everything:

So we have 3 bigger memory units: 2 `Bytes` that make a 16 bit memory unit that we call 'short' in C#, 4 `Bytes` that make a 32 bit memory unit that we call it 'int' in C#, and 8 `Bytes` that make a 64 bit memory unit, and we call it 'long' in C#.

## Step 2: What to look for?

Now that we have a simple picture of the memory in our mind, let's go back to the first picture:

I know that, you are going to say: "Hey, it's just a row of `bytes`! How to find the memory units?" And then I'll tell you that, you asked the biggest question in writing a memory scanner!

Ok, let's think that it's a part of the memory of my program, and I know, where in the memory, I have stored the `value`s and I will show you that:

As you see, a memory unit, can be stored in any part of the memory and start from any memory sector. In this program for example, I have stored a 32 bit `value` in the 0 sector, and because a 32 bit `value` takes 4 `bytes` of memory, from the sector 0 to sector 3 is assigned for a 32 bit variable in the program, and after that, from the sector 4, there is a 16 bit variable that takes 2 `bytes` of memory, next is a 64 bit variable and at the end, there is again a 16 bit variable.

Now let's think that the `value`s of the sectors are the same, but the memory units start from different sectors:

Why everything changed?
Because, a variable could be stored in any memory sector number, and most of the time, even the programmer doesn't know, where the variable is stored in the memory, and just the program knows it!

## Step 3: Where to find it?

Now, let's think that we are playing a game, and the health meter shows 83%, and we don't know the location of the variable in the memory and we want to find the variable and we start from sector 0, so the memory looks like this:

So what? Is there any 83 in the memory?
First, we know that we have the hexadecimal `value`s of the memory `bytes`. Second, we should guess the variable type to look for.

Ok, let's say that the programmers of the game have used a 32 bit (int) variable, that is the most usual data type being used for storing the `value` of the health meter. So the `value` is stored in a 4 `bytes` long part of the memory. But, how to find it?
The only way to search the memory completely, is to start from the beginning, take 4 `bytes`, test them to see if the `value` equals our digit (here 83), and find the location. Like this:

Ok, now you know the main concept of memory scanning, but there are some other things that you should know to be able to write the Memory scanner:

1. Q: How long is a program's memory? (Where to begin and where to stop?)
A: As you know, Microsoft's first OS was DOS that was a 8 bit OS, after that, the Windows 3.1 became a 16 bit OS, and after that, the Windows OS became a 32 bit OS. (I'm a real fan of Apple Co. that developed the Apple Macintosh OS, a 64 bit OS, exactly when Microsoft was working on DOS (a 8 bit OS) and today, Microsoft is going to write a 64 bit Windows (and like the first Windows versions, it still looks like the Apple OSs) but, I still recommend Apple MacOS X (Ver. 10)).
So, in the DOS OS that was a 8 bit OS, programmers named 8 bits of memory, a "Byte". After that, When the Windows 3.1 OS was a 16 bit OS, they named 16 bits of memory(2 `Bytes`) a "WORD", and 32 bits of memory(4 `Bytes`) a "DWORD"(Double Word) and 64 bits of memory(8 `Bytes`) a "QWORD"(Quad Word).
As I experienced, the length of every program's memory in Windows XP, is from "0x00000000" to the maximum `value` of a "Int"("DWORD"), and equals to "0x7FFFFFFF".
I'm not sure, but I guess, it's because of that, the Windows is a 32 bit OS and the main memory unit for it, is a 32 bit memory unit, and so, the length of a program's memory, is the maximum `value` of a 32 bit memory unit!
Ok. So, we should start our search from "0x0000000" to "0x7FFFFFFF".
2. Q: Is the first found memory address, the exact answer of our search?
A: No! As you can see, there are "0x7FFFFFFF" sectors, and when you search it for a `value` like 83, you could find so many of them. So you need to hold the memory addresses and wait for the `value`s to be changed. Then search the addresses you have, for the new `value`, and do this, until you find, just one memory address that matches your `value`.
3. Q: How to read a program's memory and search it?
A: There are some functions in Windows API that make it possible for us to read and write the memory, from another program.
Thanks goes to "Arik Poznanski" for P/Invokes and methods needed to read and write the Memory, I just used his classes to do this and didn't do the P/Invokes myself.
You can search Codeproject.com, for "Minesweeper, Behind the scenes", to find his comments about these classes.
4. Q: How to convert these `bytes` to a 16, 32 or 64 bit `value`?
A: For this, we used .NET goods! There is a class with static methods that does this for us:

```byte[] bytes = new byte[] { 0x53, 0x00, 0x00, 0x00 };
int value = System.BitConverter.ToInt32(bytes, 0);
//The value is 83
```

## Step 4: Let's do the final job

Ok, now you have all the information you need to write the memory scanner.
You just need to do these in your code:

1. Select a process to scan its memory.
2. Scan the whole memory for the specified `value` and hold the addresses.
3. Wait for the `value` to be changed and search the memory address list that you got from the first scan and again wait for the `value` to be changed and scan again, and do this until you find just the address that matches the `value`.
4. At the end, you can freeze the address with a new `value`, by using a timer to write the memory in every timer's tick.

## Comments on my classes

If you download my code, you will find them with comments for every command and every line of code. But there it a little thing I should explain:

`ReadProcessMemory(IntPtr MemoryAddress, uint bytesToRead, out int bytesRead)` that is the most important function, returns an empty `bytes` array if reading your request's size is too big! So I had to read the memory in parts as big as 20480 `bytes` (20KB), and because, when you are searching these memory parts, byte by byte, at the end of the `bytes` array, there will be some `bytes` left! (for example, 3 `bytes` will be left when you are searching for 32 bit `value`s)!

So the solution I used was this:

```if (/*scan requirement is less than 20480 bytes*/)
{
//Read the memory at once
}
else
{
/*Loop through blocks(of length 20480 bytes),
until the whole memory is read;

After the first loop, move the current address to
[Data type bytes count - 1] steps back in the memory,
to fix the previously told problem;

After the loops, check to see if any other memory addresses
are left outside of the loops and if so, read them;*/
}
```

You can see it:

## That's all

Ok folks, that's all! Hope you like and enjoy it!
And now I'm working on a Enhanced Memory Scanner that could scan all types of data, including the `Bytes`, Signed Data Types and even Strings, it just takes some time!
I'll be back soon.

## License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

## About the Author

 CEO Sweden
MVC/SPA designer and programmer.
C# programmer on .net/mono/monomac/monotouch/monodroid frameworks.
jQuery/Knockout/Angular programmer.
And has been working since 2002.

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## Comments and Discussions

 My vote of 5 Sagar (Sea)14-Dec-10 14:36 Sagar (Sea) 14-Dec-10 14:36
 Re: My vote of 5 Sojaner13-Jun-11 1:30 Sojaner 13-Jun-11 1:30
 how to scan a float value Member 456277612-Nov-10 1:46 Member 4562776 12-Nov-10 1:46
 Re: how to scan a float value Sojaner12-Nov-10 2:29 Sojaner 12-Nov-10 2:29
 My vote of 5 Baesky11-Sep-10 4:39 Baesky 11-Sep-10 4:39
 Re: My vote of 5 Member 456277612-Nov-10 1:47 Member 4562776 12-Nov-10 1:47
 Re: My vote of 5 Sojaner12-Nov-10 2:33 Sojaner 12-Nov-10 2:33
 Performance of Sojaner Scanner Cpt Balu27-Aug-10 22:30 Cpt Balu 27-Aug-10 22:30
 Hello Sojaner!I'm using your scanner in C#project for many purposes I just wrote a nice trainer game for Settlers 4. it's workflow is the following:- Reads resource informations- Create a map and places resources in correct place- Can select a resource and edit it through a simple UI- I use a simple timer for "Freeze" option which means, that amount resources can be frozen (for eg. if a settler takes a stone for construction from a 7-stone storage slot, it remains 7 after pickup)Resource read/write goes well, the only problem is gettin the list of resources.The memory block where these informations are stored can be overflown, in this case, the program continues listing anywhere. So I have to scan wide area of memory (usually 0x07000000-0x30000000)This takes much time even if scanning block's size is 20480. But this is the smaller problem, the greater problem is that I don't receive all the values. I tried other memory searchers, and I always get back more result than with this scanner. I think the problem is, that Settler's memory consist lots of block with RW permission of size from 0x4000 to 0x8000, separated with a 0x1000 sized block signed as "reserved". Maybe the reader can't read in such environment. The distance of identifiers I search is 128 bytes if they are in the same block (for eg. after loading a game).I just want to know whether I can fix it with using another parameters in opening process, freezing memory before scan or etc.Please tell me if you can advise anything.Thanks in advance:Cpt BaluHungary
 Re: Performance of Sojaner Scanner cskult26-Apr-11 10:12 cskult 26-Apr-11 10:12
 nice article! Baesky18-Aug-10 18:52 Baesky 18-Aug-10 18:52
 Re: nice article! Sojaner13-Jun-11 1:39 Sojaner 13-Jun-11 1:39
 Sojanner let see asskiller13-Mar-10 10:36 asskiller 13-Mar-10 10:36
 Re: Sojanner let see Cpt Balu27-Aug-10 22:17 Cpt Balu 27-Aug-10 22:17
 String search example required Extreme_man1-Mar-10 23:45 Extreme_man 1-Mar-10 23:45
 Re: String search example required Sojaner13-Jun-11 2:00 Sojaner 13-Jun-11 2:00
 increase speed of memory search code by over 50% rhboarder23-Sep-09 18:11 rhboarder 23-Sep-09 18:11
 i need help mansan_mansur5-Sep-09 11:13 mansan_mansur 5-Sep-09 11:13
 Need HELP!!!!!!!!!!!!! Pavel Rumberg4-Sep-09 8:40 Pavel Rumberg 4-Sep-09 8:40
 Characters and Strings? Kasperlitheater30-Jul-09 15:35 Kasperlitheater 30-Jul-09 15:35
 Re: Characters and Strings? Jordanwb27-Oct-09 17:27 Jordanwb 27-Oct-09 17:27
 Re: Characters and Strings? dzCepheus8-Oct-10 9:22 dzCepheus 8-Oct-10 9:22
 SOJANER I NEED YOUR HELP :) Goor23-Jul-09 11:29 Goor 23-Jul-09 11:29
 Re: SOJANER I NEED YOUR HELP :) Sojaner29-Jul-09 22:45 Sojaner 29-Jul-09 22:45
 ReadProcessMemory fails when pointing at protected memory The_Mega_ZZTer16-Nov-07 18:03 The_Mega_ZZTer 16-Nov-07 18:03
 Solution! The_Mega_ZZTer17-Nov-07 16:08 The_Mega_ZZTer 17-Nov-07 16:08
 Last Visit: 31-Dec-99 19:00     Last Update: 25-Feb-17 19:53 Refresh « Prev1234 Next »

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