DLL files, acronym for "Dynamic Link Library", represent a fundamental support of programming in Windows environments. This type of file is used by programs and applications to access additional functionality and data libraries without having to integrate the corresponding lines of code within them. Most often DLL files are shared by multiple programs. In most cases, the operation of DLL files is completely silent to the user and it is very rare that you need to modify the code of a DLL. However, on some occasions, you may need to register a DLL library to allow a manually installed program (or one that you created yourself) to work properly. If you enjoy programming and are passionate about this world, it might be very interesting to find out how DLL files are created.
Steps
Part 1 of 2: Using a DLL File
Step 1. Understand the nature of a DLL file
A DLL file (ie a dynamic link library) is a file intended for use on Windows systems that allows any program to call one of the functions present within it. Basically, DLL files allow the Windows operating system and all installed programs to take advantage of additional features without the latter being integrated directly into the source code of the program itself.
DLL files are essentially a fundamental part of programming in the Windows environment, the purpose of which is to lead to the creation of more streamlined, elegant and efficient programs
Step 2. Remember that the user who uses Windows or installed programs does not need to interact directly with the DLLs or even view their contents
In the vast majority of cases, the existence and functioning of DLL files is completely invisible to the end user. The programs will install the DLLs you need and use them completely automatically. For this reason, moving or deleting a DLL file could cause serious problems with the stability and functioning of programs or the operating system itself.
- Sometimes, when installing community-created programs, you may need to install the program's DLL files to a specific location. Make sure the program is safe and trustworthy before executing the instructions it gives you, as malicious code that could potentially harm your system may be hidden inside a DLL file.
- If you want to know how to create a DLL file, read the next section of the article.
Step 3. Register a new DLL
If you need to manually install a DLL by copying the corresponding file into a folder of the program that will need to use it, most likely you will also need to register it in the Windows Registry before it can be used properly. Refer to the documentation of the program itself to determine if you need to do this (it is very rare that this step has to be done manually by the user when installing a program for Windows).
- Open the "Command Prompt". The corresponding icon is visible in the "Start" menu. Alternatively, you can press the "Windows + R" key combination and type the command cmd. Navigate to the folder where you copied the new DLL file.
- If you are using a computer running Windows 7 or a later version, access the folder that contains the DLL library to register, hold down the "Shift" key while right-clicking on an empty spot inside the folder, then select the "Open command window here" option. A new "Command Prompt" window will appear which will point directly to the folder of the new DLL.
- Type the command regsvr32 [DLLName].dll and press the "Enter" key. The DLL file in question will be registered in the Windows registry.
- Type the command regsvr32 -u [DLLname].dll and press the "Enter" key to delete the DLL file in question from the Windows registry.
Part 2 of 2: Decompile a Reverse Engineering (DLL) file
Step 1. Download and install a decompiler
It is a program capable of reconstructing the source code of a file or program, in this case a DLL library, starting from the compiled version. In order to go back to the source code (i.e. the human-readable and understandable code) of a compiled DLL file (the version running and used by programs that have access to the library), you need to use a decompiler to execute the process that is called "reverse engineering". If you try to open a DLL file using a regular program, such as Notepad, it will simply display a series of nonsensical random characters.
dotPeek is one of the best known and most used free decompilers. You can download the installation file from this URL: jetbrains.com/decompiler/
Step 2. Open the DLL file using the decompiler of your choice
If you are using dotPeek, click on the "File" menu, choose the "Open" option and finally click on the DLL file you want to decompile. You will be able to examine the contents of the DLL library you have chosen without affecting the functioning of the system.
Step 3. Use the "Assembly Explorer" window to browse the nodes that make up the DLL file
DLL libraries are made up of "nodes" or code modules that work in synergy to give life to the DLL itself. You have the option to expand each node to view the code modules it contains.
Step 4. Double click on a node to view the corresponding source code
The latter will appear in the right pane of the dotPeek window. This way you can go through the source code to examine it and understand how it works. DotPeek displays the code in the form of the C # language. Alternatively, the program will automatically download the additional libraries to view the source code written with another programming language.
If the node you selected requires the use of other libraries to view the source code, dotPeek will automatically download them
Step 5. Get the explanations of the pieces of code you want
If you have encountered a piece of code that you do not understand how it works or what it means, you can solve the problem using the "Quick Documentation" feature.
- Place the cursor of the text in the point of the code, displayed in the "Code Viewer" window, of which you need to consult the documentation;
- Press the key combination "Ctrl + Q" to open the "Quick Documentation" window;
- Follow the links in the documentation to learn more about the topics and understand all aspects related to the code you are studying.
Step 6. Export the source code as a project for Visual Studio
If you need to modify the source code, add other functions and recompile it, you can export the DLL code to a Visual Studio compatible format. The code will be exported to C #, even if it was originally written in a different programming language.
- Select the DLL file displayed in the "Assembly Explorer" window with the right mouse button;
- Select the "Export to Project" option;
- Choose your export options. If you need to immediately edit the DLL file you exported, you can open the corresponding project directly in Visual Studio.
Step 7. Edit the code using Visual Studio
After the project has been opened within Visual Studio, you will have complete control of the corresponding source code, so you can modify it to your liking and create your own customized version of the original DLL. Read this article for more information on how to use Visual Studio.
