How to Create DLL Files

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DLL files are dynamic-linked library files written and controlled with C++. DLLs make sharing, storing, and saving your code simple. This wikiHow will show you how to create a DLL file with Visual Studio , the Windows application, or Visual Studio for Mac. Make sure you have “Desktop Development with C++” checked when you install. If you already have Visual Studio but didn’t check that box, you can run the installer again to make sure you do.

Making and Using a Dynamic Link Library

  • To make a DLL, open Visual Studio and start a new project for C++. Set the project type as Library .
  • Click Dynamic-link Library (DLL) and create it. Add the code from the Microsoft website.
  • Add a CPP file to the DLL, and then select Build Solution .

Steps

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  1. You can find this in your Start Menu or Applications folder. Since a DLL is a library of information, it is only one piece of a project, and usually requires an accompanying app to access it.
  2. You’ll find this either above the project space (Windows) or along the top of your screen (Macs). [1]
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  3. The “Create a New Project” dialog box will pop up. [2]
  4. These will filter what kinds of project templates appear.
    • Click Language to get a drop-down menu and click C++ .
  6. [3]
  7. Your choice will highlight blue. Click Next to continue. [4]
  8. For example, type “MathLibrary” in the box for a sample name. [5]
  9. The DLL project is created. [6]
  10. You can do this by clicking “ Add New Item ” from “ Project ” in the menu bar.
    • Select Visual C++ from the left menu of the dialog box.
    • Select Header file (.h) from the center of the dialog box.
    • Type the name as “MathLibrary.h” in the name field below the menu choices.
    • Click Add to generate the blank header file.
    11.  // MathLibrary.h - Contains declarations of math functions 
 #pragma once 
 #ifdef MATHLIBRARY_EXPORTS 
 #define MATHLIBRARY_API __declspec(dllexport) 
 #else 
 #define MATHLIBRARY_API __declspec(dllimport) 
 #endif 
 // The Fibonacci recurrence relation describes a sequence F 
 // where F(n) is { n = 0, a 
 //               { n = 1, b 
 //               { n > 1, F(n-2) + F(n-1) 
 // for some initial integral values a and b. 
 // If the sequence is initialized F(0) = 1, F(1) = 1, 
 // then this relation produces the well-known Fibonacci 
 // sequence: 1, 1, 2, 3, 5, 8, 13, 21, 34, ... 
 // Initialize a Fibonacci relation sequence 
 // such that F(0) = a, F(1) = b. 
 // This function must be called before any other function. 
 extern 
 "C" 
 MATHLIBRARY_API 
 void 
 fibonacci_init 
 ( 
 const 
 unsigned 
 long 
 long 
 a 
 , 
 const 
 unsigned 
 long 
 long 
 b 
 ); 
 // Produce the next value in the sequence. 
 // Returns true on success and updates current value and index; 
 // false on overflow, leaves current value and index unchanged. 
 extern 
 "C" 
 MATHLIBRARY_API 
 bool 
 fibonacci_next 
 (); 
 // Get the current value in the sequence. 
 extern 
 "C" 
 MATHLIBRARY_API 
 unsigned 
 long 
 long 
 fibonacci_current 
 (); 
 // Get the position of the current value in the sequence. 
 extern 
 "C" 
 MATHLIBRARY_API 
 unsigned 
 fibonacci_index 
 ();
    • This is sample code provided from the Microsoft help website.
  12. You can do this by clicking Add New Item from “Project” in the menu bar.
    • Select “ Visual C++ ” from the left menu of the dialog box.
    • Select “ C++ File (.cpp) ” from the center of the dialog box.
    • Type the name as “MathLibrary.cpp” in the name field below the menu choices.
    • Click Add to generate the blank file.
    13.  // MathLibrary.cpp : Defines the exported functions for the DLL. 
 #include 
 "stdafx.h" // use pch.h in Visual Studio 2019 
  
 #include 
 <utility> 
  
 #include 
 <limits.h> 
  
 #include 
 "MathLibrary.h" 
  
 // DLL internal state variables: 
 static 
 unsigned 
 long 
 long 
 previous_ 
 ; 
 // Previous value, if any 
 static 
 unsigned 
 long 
 long 
 current_ 
 ; 
 // Current sequence value 
 static 
 unsigned 
 index_ 
 ; 
 // Current seq. position 
 // Initialize a Fibonacci relation sequence 
 // such that F(0) = a, F(1) = b. 
 // This function must be called before any other function. 
 void 
 fibonacci_init 
 ( 
 const 
 unsigned 
 long 
 long 
 a 
 , 
 const 
 unsigned 
 long 
 long 
 b 
 ) 
 { 
 index_ 
 = 
 0 
 ; 
 current_ 
 = 
 a 
 ; 
 previous_ 
 = 
 b 
 ; 
 // see special case when initialized 
 } 
 // Produce the next value in the sequence. 
 // Returns true on success, false on overflow. 
 bool 
 fibonacci_next 
 () 
 { 
 // check to see if we'd overflow result or position 
 if 
 (( 
 ULLONG_MAX 
 - 
 previous_ 
 < 
 current_ 
 ) 
 || 
 ( 
 UINT_MAX 
 == 
 index_ 
 )) 
 { 
 return 
 false 
 ; 
 } 
 // Special case when index == 0, just return b value 
 if 
 ( 
 index_ 
 > 
 0 
 ) 
 { 
 // otherwise, calculate next sequence value 
 previous_ 
 += 
 current_ 
 ; 
 } 
 std 
 :: 
 swap 
 ( 
 current_ 
 , 
 previous_ 
 ); 
 ++ 
 index_ 
 ; 
 return 
 true 
 ; 
 } 
 // Get the current value in the sequence. 
 unsigned 
 long 
 long 
 fibonacci_current 
 () 
 { 
 return 
 current_ 
 ; 
 } 
 // Get the current index position in the sequence. 
 unsigned 
 fibonacci_index 
 () 
 { 
 return 
 index_ 
 ; 
 }
    • This is sample code provided from the Microsoft help website.
  14. You’ll find this either above the project space (Windows) or along the top of your screen (Macs).
  15. After you click that, you should see text similar to this: 
       1 
 >------ 
 Build 
 started 
 : 
 Project 
 : 
 MathLibrary 
 , 
 Configuration 
 : 
 Debug 
 Win32 
 
       
 1 
 > 
 MathLibrary 
 . 
 cpp 
 1 
 > 
 dllmain 
 . 
 cpp 
 1 
 > 
 Generating 
 Code 
 ... 
 1 
 > 
 Creating 
 library 
 C 
 : 
 \ 
 Users 
 \ 
 username 
 \ 
 Source 
 \ 
 Repos 
 \ 
 MathLibrary 
 \ 
 Debug 
 \ 
 MathLibrary 
 . 
 lib 
 and 
 object 
 C 
 : 
 \ 
 Users 
 \ 
 username 
 \ 
 Source 
 \ 
 Repos 
 \ 
 MathLibrary 
 \ 
 Debug 
 \ 
 MathLibrary 
 . 
 exp 
 1 
 > 
 MathLibrary 
 . 
 vcxproj 
 -> 
 C 
 : 
 \ 
 Users 
 \ 
 username 
 \ 
 Source 
 \ 
 Repos 
 \ 
 MathLibrary 
 \ 
 Debug 
 \ 
 MathLibrary 
 . 
 dll 
 1 
 > 
 MathLibrary 
 . 
 vcxproj 
 -> 
 C 
 : 
 \ 
 Users 
 \ 
 username 
 \ 
 Source 
 \ 
 Repos 
 \ 
 MathLibrary 
 \ 
 Debug 
 \ 
 MathLibrary 
 . 
 pdb 
 ( 
 Partial 
 PDB 
 ) 
 ========== 
 Build 
 : 
 1 
 succeeded 
 , 
 0 
 failed 
 , 
 0 
 up 
 - 
 to 
 - 
 date 
 , 
 0 
 skipped 
 ==========
    • If your DLL creation was successful, you'll see that here. If there was an error, it will be listed here for you to fix.
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      References

      1. ↑ https://learn.microsoft.com/en-us/cpp/build/walkthrough-creating-and-using-a-dynamic-link-library-cpp?view=msvc-170
      2. ↑ https://learn.microsoft.com/en-us/cpp/build/walkthrough-creating-and-using-a-dynamic-link-library-cpp?view=msvc-170
      3. ↑ https://learn.microsoft.com/en-us/cpp/build/walkthrough-creating-and-using-a-dynamic-link-library-cpp?view=msvc-170
      4. ↑ https://learn.microsoft.com/en-us/cpp/build/walkthrough-creating-and-using-a-dynamic-link-library-cpp?view=msvc-170
      5. ↑ https://learn.microsoft.com/en-us/cpp/build/walkthrough-creating-and-using-a-dynamic-link-library-cpp?view=msvc-170
      6. ↑ https://learn.microsoft.com/en-us/cpp/build/walkthrough-creating-and-using-a-dynamic-link-library-cpp?view=msvc-170

      About This Article

      Article Summary X

      1. Open Visual Studio.
      2. Open a new Dynamic-link library (DLL) project.
      3. Add a header file.
      4. Add a CPP file.
      5. Check to see if the library works.

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