Creating a DLL using Visual C: A Step-by-Step Guide

It explains how to create and use a dll. The most important thing is to create a New project and then select a Win32 Console Application. Afterwards, in the Application Settings page, under Application type, you have to select DLL.

Static linking copies all the object code in a static library into the executables that use it when they're built. Dynamic linking includes only the information needed by Windows at run time to locate and load the DLL that contains a data item or function. When you create a DLL, you also create an import library that contains this information. When you build an executable that calls the DLL, the linker uses the exported symbols in the import library to store this information for the Windows loader. When the loader loads a DLL, the DLL is mapped into the memory space of your application. If present, a special function in the DLL, DllMain, is called to do any initialization the DLL requires.

how to create a dll using visual c

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Dynamic linking saves memory and reduces swapping. Many processes can use a DLL simultaneously, sharing a single copy of the read-only parts of a DLL in memory. In contrast, every application that is built by using a statically linked library has a complete copy of the library code that Windows must load into memory.

Dynamic linking saves disk space and bandwidth. Many applications can share a single copy of the DLL on disk. In contrast, each application built by using a static link library has the library code linked into its executable image. That uses more disk space, and takes more bandwidth to transfer.

Dynamic linking makes creation of international versions of your application easier. DLLs are a convenient way to supply locale-specific resources, which make it much easier to create international versions of an application. Instead of shipping many localized versions of your application, you can place the strings and images for each language in a separate resource DLL. Then your application can load the appropriate resources for that locale at runtime.

A potential disadvantage to using DLLs is that the application isn't self-contained. It depends on the existence of a separate DLL module: one that you must deploy or verify yourself as part of your installation.

This step-by-step walkthrough shows how to use the Visual Studio IDE to create your own dynamic link library (DLL) written in Microsoft C++ (MSVC). Then it shows how to use the DLL from another C++ app. DLLs (also known as shared libraries in UNIX-based operating systems) are one of the most useful kinds of Windows components. You can use them as a way to share code and resources, and to shrink the size of your apps. DLLs can even make it easier to service and extend your apps.

In this walkthrough, you'll create a DLL that implements some math functions. Then you'll create a console app that uses the functions from the DLL. You'll also get an introduction to some of the programming techniques and conventions used in Windows DLLs.

This walkthrough creates two Visual Studio solutions; one that builds the DLL, and one that builds the client app. The DLL uses the C calling convention. It can be called from apps written in other programming languages, as long as the platform, calling conventions, and linking conventions match. The client app uses implicit linking, where Windows links the app to the DLL at load-time. This linking lets the app call the DLL-supplied functions just like the functions in a statically linked library.

This walkthrough doesn't cover some common situations. The code doesn't show the use of C++ DLLs by other programming languages. It doesn't show how to create a resource-only DLL, or how to use explicit linking to load DLLs at run-time rather than at load-time. Rest assured, you can use MSVC and Visual Studio to do all these things.

For links to more information about DLLs, see Create C/C++ DLLs in Visual Studio. For more information about implicit linking and explicit linking, see Determine which linking method to use. For information about creating C++ DLLs for use with programming languages that use C-language linkage conventions, see Exporting C++ functions for use in C-language executables. For information about how to create DLLs for use with .NET languages, see Calling DLL Functions from Visual Basic Applications.

This walkthrough assumes you're using Visual Studio 2017 version 15.9 or later. Some earlier versions of Visual Studio 2017 had defects in the code templates, or used different user interface dialogs. To avoid problems, use the Visual Studio Installer to update Visual Studio 2017 to version 15.9 or later.

In this set of tasks, you create a project for your DLL, add code, and build it. To begin, start the Visual Studio IDE, and sign in if you need to. The instructions vary slightly depending on which version of Visual Studio you're using. Make sure you have the correct version selected in the control in the upper left of this page.

To verify that everything works so far, compile the dynamic link library. To compile, choose Build > Build Solution on the menu bar. The DLL and related compiler output are placed in a folder called Debug directly below the solution folder. If you create a Release build, the output is placed in a folder called Release. The output should look something like this:

When you create a DLL, think about how client apps may use it. To call the functions or access the data exported by a DLL, client source code must have the declarations available at compile time. At link time, the linker requires information to resolve the function calls or data accesses. A DLL supplies this information in an import library, a file that contains information about how to find the functions and data, instead of the actual code. And at run time, the DLL must be available to the client, in a location that the operating system can find.

A minimal console application project is created for you. The name for the main source file is the same as the project name that you entered earlier. In this example, it's named MathClient.cpp. You can build it, but it doesn't use your DLL yet.

When the wizard finishes, a minimal console application project is created for you. The name for the main source file is the same as the project name that you entered earlier. In this example, it's named MathClient.cpp. You can build it, but it doesn't use your DLL yet.

Double-click in the top pane of the Additional Library Directories dialog box to enable an edit control. In the edit control, specify the path to the location of the MathLibrary.lib file. By default, it's in a folder called Debug directly under the DLL solution folder. If you create a release build, the file is placed in a folder called Release. You can use the $(IntDir) macro so that the linker can find your DLL, no matter which kind of build you create. If you followed the directions to put your client project in a separate solution from the DLL project, the relative path should look like this:

Congratulations, you've created an application that calls functions in your DLL. Now run your application to see what it does. On the menu bar, choose Debug > Start Without Debugging. Visual Studio opens a command window for the program to run in. The last part of the output should look like:

Now that you've created a DLL and a client application, you can experiment. Try setting breakpoints in the code of the client app, and run the app in the debugger. See what happens when you step into a library call. Add other functions to the library, or write another client app that uses your DLL.

Note: When you have created a DLL project then automatically PROJECTNAME_EXPORTS is defined in preprocessor symbols of the DLL project. In this example, CALCULATIONDLL_EXPORTS is defined when your CALCULATIONDLL DLL project is built.

You may also want to review the setting Common Language Runtime Support. If enabled (switch /clr), this will allow you to create .NET classes in this project. For a pure C++ project, however, you may want to disable CLR support (as shown in the screenshot above).

Hi, I have made some progress, again thanks to your guidance above. After a LOT of fiddling and trial and error, have created both a function as a .dll and as a .lib and have been able to write small C++ console programs to use them

Register and use a Microsoft Visual C/C++ (MSVC) toolchain running on a 64-bit Windows platform to compile a 32-bit dynamic link library (DLL). This example uses a Microsoft compiler. However, the concepts and programming interface apply for other toolchains. Once you register the toolchain, you can select it from a list of toolchains, and the code generator generates a makefile to build the code by using that toolchain. A toolchain consists of several tools, such as a compiler, linker, and archiver with multiple different configuration options. The toolchain compiles, links, and runs code on a specified platform. To access the files that this example uses, click Open Script.

If you are not using a Windows platform, or if you do not have a supported version of Microsoft Visual C/C++, the example generates only code and a makefile, without running the generated makefile.

To generate the 32-bit dynamic link library (DLL), create a 'dll' code generation configuration object. Specifying 'dll' directs the linker (a build tool in the toolchain) to use "Shared Library" linker commands.

If you have a supported version of the compiler installed, you can build the 32-bit executable by using a C main function. You can use the executable to test that the generated code works as expected. 2ff7e9595c