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Example 1 : Working from the command lineNow we make a one-line DLL. Here's the source:
Save this to file myfun.cpp and compile it from the DOS prompt with
The -LD switch says to generate a DLL. Next we make an executable which calls the DLL. Here's the source:
Save this to file main.cpp. Then compile and link from the command prompt with
Execute it from the command line (just type 'main') and watch with awe! Example 2 : Using VC++ IDE to create DLLThe DLL entry pointWhen 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. WARNING: 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. Exporting DLL functionsTo export DLL functions, you can either add a function keyword to the exported DLL functions or create a module definition (.def) file that lists the exported DLL functions. To use a function keyword, you must declare each function that you want to export with the following keyword:
To use exported DLL functions in the application, you must declare each function that you want to import with the following keyword:
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. In the module definition file, you declare the LIBRARY statement and the EXPORTS statement for the DLL. The following code is an example of a definition file.
Write Sample DLLIn Microsoft Visual C++ 6.0, you can create a DLL by selecting either the Win32 Dynamic-Link Library project type or the MFC AppWizard (dll) project type. The following code is an example of a DLL that was created in Visual C++ by using the Win32 Dynamic-Link Library project type.
Calling Sample DLL in your ProgramThe following code is an example of a Win32 Application project that calls the exported DLL function in the SampleDLL DLL.
NOTE: In load-time dynamic linking, you must link the SampleDLL.lib import library that is created when you build the SampleDLL project. In run-time dynamic linking, you use code that is similar to the following code to call the SampleDLL.dll exported DLL function.
When you compile and link the SampleDLL application, the Windows operating system searches for the SampleDLL DLL in the following locations in this order:
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