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Linking is often referred to as a process that is performed when the executable is compiled, while a dynamic linker is a special part of an operating system that loads external shared libraries into a running process and then binds those shared libraries dynamically to the running process. This approach is also called dynamic linking or late ...
A dynamic-link library (DLL) is a shared library in the Microsoft Windows or OS/2 operating system. A DLL can contain executable code (functions), data , and resources . A DLL file often has file extension .dll even though this is not required.
A program that is configured to use a library can use either static-linking or dynamic-linking.Historically, libraries could only be static. [4] For static-linking (), the library is effectively embedded into the programs executable file, while for dynamic-linking the library can be loaded at runtime from a shared location, such as system files.
The Windows operating system contains compiled versions of these libraries known as dynamically-linked libraries (), which are executable libraries that can be used by multiple programs while only one copy of the library is loaded into memory.
A filename typically starts with lib, and ends with .a for a static library or .so for a shared object (dynamically linked library). For example, libfoo.a and libfoo.so . Often, symbolic link files are used to manage versioning of a library by providing a link file named without a version that links to a file named with a version.
Dynamic linking offers three advantages: Often-used libraries (for example the standard system library) need to be stored in only one location, not duplicated in every single binary. If a library is upgraded or replaced, all programs using it dynamically will immediately benefit from the corrections. Static builds would have to be re-linked first.
Dynamic loading is a mechanism by which a computer program can, at run time, load a library (or other binary) into memory, retrieve the addresses of functions and variables contained in the library, execute those functions or access those variables, and unload the library from memory.
The invention of dynamic address translation (the function provided by an MMU) originally reduced the need for position-independent code because every process could have its own independent address space (range of addresses). However, multiple simultaneous jobs using the same code created a waste of physical memory.