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<title>Terminology</title> |
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<h2 align="center">Terminology</h2> |
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<h3>Introduction</h3> |
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When discussing Derelict in the |
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<a href="http://www.dsource.org/forums/viewforum.php?f=19&sid=d6f86cfb804d7c8727af1f58cd327d2c">project forums</a> |
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or elsewhere, it is important to understand the terminology that often surfaces |
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in such discussions. This will also be helpful in better understanding the Derelict |
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documentation. Following is a list of terms which could potentially be misunderstood |
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and their meaning when used in relation to Derelict. |
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<h4>Shared Library</h4> |
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This term is a platform-agnostic way of describing a library which is dynamically |
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loaded at run time and can be used simultaneously by multiple programs. On Windows, |
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such libraries are referred to as "Dynamic Link Libraries", or "DLLs", and have |
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the .dll file extension. On Linux and other Unix-like platforms, such libraries |
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are referred to as "Shared Object Libraries" or "Shared Objects" and have the |
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file extension of .so. This also includes the "Frameworks" found on Mac. |
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<p> |
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When this term is used in relation to Derelict, it can be considered to refer to |
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any of the above library formats. When you need to refer to a specific |
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format, you should use the format name instead of the term "Shared Library". |
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</p> |
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<h4>Static Libraries</h4> |
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Static libraries are the traditional form of distribution for archived object |
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files. On Windows, such libraries are called "Libraries" and have the extension |
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.lib. On Linux and other Unix-like platforms, such libraries are called "object |
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archives", "archives", "libraries", and several other terms, all of which have |
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the file extension .a and usually have the prefix "lib" prepended to the file |
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name. |
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<p> |
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Static libraries are compiled into the application at compile time, rather |
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than being loaded at run time. Because the library is compiled into the executable, |
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no other executable can share the same compilation. |
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</p> |
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<h4>Import Libraries, or Static Import Libraries</h4> |
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An import library is a library which automates the process of loading a shared |
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library. On Windows, when you create a DLL most compilers also create a static |
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library by the same name. This library is the DLL's import library. By compiling |
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this library into your executable, the application will be bound to the DLL and |
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the DLL will be loaded at run time by the OS. |
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<p> |
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Linux and other Unix-like platforms handle this differently. Rather than link |
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to a separate, static import library, you link to the .so itself. In otherwords, |
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the .so doubles as a shared library and as an import library. Even though you |
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are linking to the .so at compile time, the library itself is still loaded at |
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run time. |
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</p> |
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<h4>Dynamic Linkage</h4> |
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The term "dynamic linkage" usually refers to linking with an import library. As |
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described above, the import library may be a static library (as on Windows), or |
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may be the shared library itself (as on Linux). |
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<h4>Static Linkage</h4> |
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The term "static linkage" refers to linking with a static library at compilation |
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time: .lib on Windows and .a on Linux. Technically speaking, an import library |
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on Windows must be "statically linked", but the term is normally not applied to |
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import libraries. |
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<h4>Dynamic Loading</h4> |
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In the context of Derelict, "dynamic loading" refers to the normal method of |
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loading a shared library at run time: you link with an import library and the |
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operating system loads the library when the application starts. You, as the |
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programmer, need do nothing programmatically to load the shared library. |
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<h4>Manual Loading</h4> |
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In the context of Derelict, "manual loading" refers to bypassing the normal |
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method of loading a shared library at run time: you do not link with an import |
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library and, instead, load the shared library programmatically through |
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operating system API calls. This is Derelict's mode of operation and is the |
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reason why you must call methods like Derelict*.load(). |
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