Why dlls are used

DLL Dynamic link libraries are files that contain data, code, or resources needed for the running of applications. These are files that are created by the windows ecosystem and can be shared between two or more applications. When a program or software runs on Windows, much of how the application works depends on the DLL files of the program.

For instance, if a particular application had several modules, then how each module interacts with each other is determined by the Windows DLL files. What are dll files , About Dll files. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. What exactly are DLL files, and how do they work?

Ask Question. Asked 13 years, 1 month ago. Active 1 year, 10 months ago. Viewed k times. So, what's the deal with them? Improve this question. Alan 2 2 silver badges 14 14 bronze badges.

Since this is only tagged with Windows, and this question was written back in , it's worth to mention that nowadays dll's run on Mac and Linux too with. NET Core.

Add a comment. Active Oldest Votes. What is a DLL? What does a DLL contain? Types of libraries: On virtually all operating systems, there are 2 types of libraries. More on static and dynamic libraries: You don't normally see static libraries though on your computer, because a static library is embedded directly inside of a module EXE or DLL. Improve this answer. Brian R. Bondy Brian R. Bondy k gold badges silver badges bronze badges.

Should probably mention the import lib somewhere. OK I'll go away now. Removed those that seem to be addressed. How do I get points for this? Brian Should. Or is it language independent?

Are they important? Installed applications also use DLL files DLL files also becomes a form of separating functionalities physically as explained above.

DLL Hell However, at times system upgrades often breaks other programs when there is a version mismatch between the shared DLL files and the program that requires them. How do we know what's inside a DLL file?

Yogesh Umesh Vaity Please complete this sentence "The. RehanKhan Starting with. Did you know this information about DLL files? Is there something important missing from this article? Let us know in the comments. By signing up, you agree to our Privacy Policy and European users agree to the data transfer policy. Diogo diogocostaweb is a Biologist with a grip on computers and technology.

Running Windows systems all his life, has a big interest in discovering new apps that increase productivity or simply make things more interesting. He lives in Portugal and has photography and music as main hobbies. He is also the author of the page techkern. A very simplistic explanation. Where can I find a list of DLLs for a given program? I remember once seeing a program that will provide this. Here Are 12 Fixes. Affiliate Disclosure: Make Tech Easier may earn commission on products purchased through our links, which supports the work we do for our readers.

DLL Files? Is this article useful? This utility compares the DLLs that are listed in two text files and produces a third text file that contains the differences. This utility loads the text files that are created by using the Dlister. This section describes the issues and the requirements that you should consider when you develop your own DLLs.

The two methods of linking are load-time dynamic linking and run-time dynamic linking. In load-time dynamic linking, an application makes explicit calls to exported DLL functions like local functions. To use load-time dynamic linking, provide a header.

When you do this, the linker will provide the system with the information that is required to load the DLL and resolve the exported DLL function locations at load time. When you use run-time dynamic linking, you do not need an import library file. The following list describes the application criteria for when to use load-time dynamic linking and when to use run-time dynamic linking:. If the initial startup performance of the application is important, you should use run-time dynamic linking.

In load-time dynamic linking, the exported DLL functions are like local functions. This makes it easy for you to call these functions. In run-time dynamic linking, an application can branch to load different modules as required. It is important when you develop multiple-language versions. When you create a DLL, you can optionally specify an entry point function.

The entry point function is called when processes or threads attach themselves to the DLL or detached themselves from the DLL. You can use the entry point function to initialize data structures or to destroy data structures as required by the DLL. Additionally, if the application is multithreaded, you can use thread local storage TLS to allocate memory that is private to each thread in the entry point function.

The following code is an example of the DLL entry point function. When the entry point function returns a FALSE value, the application will not start if you are using load-time dynamic linking. If you are using run-time dynamic linking, only the individual DLL will not load. The entry point function should only perform simple initialization tasks and should not call any other DLL loading or termination functions.

For example, in the entry point function, you should not directly or indirectly call the LoadLibrary function or the LoadLibraryEx function. Additionally, you should not call the FreeLibrary function when the process is terminating. In multithreaded applications, make sure that access to the DLL global data is synchronized thread safe to avoid possible data corruption.

To do this, use TLS to provide unique data for each thread. To export DLL functions, you can either add a function keyword to the exported DLL functions or create a module definition.

Typically, you would use one header file that has a define statement and an ifdef statement to separate the export statement and the import statement. You can also use a module definition file to declare exported DLL functions.

When you use a module definition file, you do not have to add the function keyword to the exported DLL functions. The following code is an example of a definition file. In load-time dynamic linking, you must link the SampleDLL. In run-time dynamic linking, you use code that is similar to the following code to call the SampleDLL. With the introduction of. NET and the. An assembly is a logical unit of functionality that runs under the control of the. An assembly physically exists as a.

An assembly file contains an assembly manifest, type metadata, Microsoft intermediate language MSIL code, and other resources. The assembly manifest contains the assembly metadata that provides all the information that is required for an assembly to be self-describing. The following information is included in the assembly manifest:. The MSIL code that is contained in the assembly cannot be directly executed. By default, when you create an assembly, the assembly is private to the application.

To create a shared assembly requires that you assign a strong name to the assembly and then publish the assembly in the global assembly cache. The following list describes some of the features of assemblies compared to the features of Win32 DLLs:.

When you create an assembly, all the information that is required for the CLR to run the assembly is contained in the assembly manifest. The assembly manifest contains a list of the dependent assemblies. Therefore, the CLR can maintain a consistent set of assemblies that are used in the application.

In an assembly manifest, version information is recorded and enforced by the CLR. Additionally, version policies let you enforce version-specific usage. In Win32 DLLs, versioning can't be enforced by the operating system.