What Is a DLL File? (With Types, Advantages and Example)

Linking is part of the process of creating a computer program in which programmers combine their new program codes with preexisting code libraries (special functions, such as printing a document, that are used often). Static linking, the process traditionally used in many operating systems, puts everything together into the executable program. Dynamic linking, on the other hand, stores code libraries in DLL files. The functions in these files are then accessed by different running programs only when needed. Dynamic linking results in programs that use less memory and disk space and that are easier to upgrade. Without dynamic linking, making changes to part of a code library—for example, a dialog box for saving a file—would mean making changes to every statically linked program that uses it. With dynamic linking, only the DLL needs to be changed.

Despite these advantages, dynamic linking has some trade-offs. Gains in efficiency are sometimes offset by losses in the stability of a program. In the past a newly installed program might occasionally have replaced an existing DLL, which sometimes caused existing programs to crash or behave oddly, a situation programmers call “DLL hell.” To avoid these problems, Windows relies on protected DLLs and Windows file protection (WFP). Protected DLLs are updated only by Microsoft, and if one is replaced by some other source, Windows reverts the DLL back to the original version. An official update can still introduce bugs, though it is unlikely to do so.

What Are DLLs?

Features of DLL files

There are some key features of DLL files that people commonly use:

What is a DLL file?

DLL files are ones that contain instructions to command several different computer programs to perform tasks. For example, many operating systems use DLL files to function and can use these to complete tasks like finding files or storage space. DLL files have written code inside that command the different applications to perform actions. On an operating system, this might look like functions like opening or closing windows for unique programs. As this file type supports other applications, using one has several dependencies:

There are several ways to work around file dependencies, like file protection methods and private DLLs that allow you to temporarily disconnect DLLs from other programs and update the version to maintain proper functioning.

Advantages of DLL files

There are several advantages of DLL files

Reduced memory use

DLL files have a library of functions that devices can use across programs. By reusing these, instead of them working independently in each program, the applications you use can run faster. This can also help device memory as it might not need to run different commands on background application, improving overall device health and speed.

Simplified structure creation

This file type enables you to use dynamic applications with a modular structure. This means that many times a single program might run several modules at once. With this, you can create larger programs or ones that require several programming languages and it can still produce a positive user experience.

Easy installation

When you install a DLL file, it can instruct several programs to perform actions. Rather than hard-coding individual files and commands into each, this makes it easier to install and maintain. When you make updates to the functions within a DLL file, it can automatically send the updated commands to the different programs it uses. This can mean you can have updated applications that are free from bugs, which can be common if you use third-party DLL files.

Types of DLL files

Though many types of DLL files end in a .dll extension, some have other extensions to perform unique functions. These are similar to executable files, or .exe files, that you use to perform certain actions on your device. There are several other types of DLL files:

Coded sample of a DLL file

Heres a sample of a coded DLL file made using the programming language C++:

// SampleDLL.cpp

#include “stdafx.h”
#include “sampleDLL.h”
BOOL APIENTRY DllMain( HANDLE hModule, DWORD ul_reason_for_call, LPVOID lpReserved
return TRUE;

void HelloWorld()
MessageBox( NULL, TEXT(“Hello World”), TEXT(“In a DLL”), MB_OK);

// File: SampleDLL.h
#ifndef INDLL_H
#define INDLL_H
extern __declspec(dllexport) void HelloWorld();
extern __declspec(dllimport) void HelloWorld();


With the following example, you can find code that can recognize a defined DLL function in a Win32 Application:

// SampleApp.cpp


#include “stdafx.h”

#include “sampleDLL.h”

int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)



return 0;


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What is DLL file used for?

DLL advantages
  • Uses fewer resources. When multiple programs use the same library of functions, a DLL can reduce the duplication of code that is loaded on the disk and in physical memory. …
  • Promotes modular architecture. A DLL helps promote developing modular programs. …
  • Eases deployment and installation.

What is an example of a DLL file?

There are two types of DLLs: simple and complex. A simple DLL contains only DLL code in which special code sequences are generated by the compiler for referencing functions and external variables, and using function pointers.

What is a DLL file and how do I open it?

A DLL is a library that contains code and data that can be used by more than one program at the same time. For example, in Windows operating systems, the Comdlg32 DLL performs common dialog box related functions. Each program can use the functionality that is contained in this DLL to implement an Open dialog box.

Should I delete DLL files?

Examples of such DLLs include icon libraries, sometimes having the extension ICL , and font files, having the extensions FON and FOT .

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