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In computing, a library is a collection of System resource that can be used during software development to implement a computer program. Commonly, a library consists of executable code such as compiled functions and classes, or a library can be a collection of source code. A resource library may contain data such as and Text string.
A library can be used by multiple, independent consumers (programs and other libraries). This differs from resources defined in a program which can usually only be used by that program. When a consumer uses a library resource, it gains the value of the library without having to implement it itself. Libraries encourage software reuse in a modular fashion. Libraries can use other libraries resulting in a hierarchy of libraries in a program.
When writing code that uses a library, a programmer only needs to know how to use it, its application programming interface (API) not its internal details. For example, a program could use a library that abstracts a complicated system call so that the programmer can use the system feature without spending time to learn the intricacies of the system function.
In 1947 Herman Goldstine and von Neumann speculated that it would be useful to create a "library" of for their work on the IAS machine, an early computer that was not yet operational at that time. They envisioned a physical library of magnetic wire recordings, with each wire storing reusable computer code.
Inspired by von Neumann, Maurice Wilkes and his team constructed EDSAC. A filing cabinet of punched tape held the subroutine library for this computer. Programs for EDSAC consisted of a main program and a sequence of subroutines copied from the subroutine library. In 1951 the team published the first textbook on programming, The Preparation of Programs for an Electronic Digital Computer, which detailed the creation and the purpose of the library.
COBOL included "primitive capabilities for a library system" in 1959,Richard Wexelblat (1981). 9780127450407, Academic Press (A subsidiary of Harcourt Brace). . ISBN 9780127450407 but Jean Sammet described them as "inadequate library facilities" in retrospect.Wexelblat, op. cit., p. 258
JOVIAL has a Communication Pool (COMPOOL), roughly a library of header files.
Another major contributor to the modern library concept came in the form of the subprogram innovation of FORTRAN. FORTRAN subprograms can be compiled independently of each other, but the compiler lacked a linker. So prior to the introduction of modules in Fortran-90, type checking between FORTRANIt was possible earlier between, e.g., Ada subprograms. subprograms was impossible. (1988). 9780201184839, Addison-Wesley. ISBN 9780201184839
By the mid 1960s, copy and macro libraries for assemblers were common. Starting with the popularity of the IBM System/360, libraries containing other types of text elements, e.g., system parameters, also became common.
In IBM's OS/360 and its successors this is called a partitioned data set.
The first object-oriented programming language, Simula, developed in 1965, supported adding classes to libraries via its compiler.Wilson and Clark, op. cit., p. 52Wexelblat, op. cit., p. 716
Static linking is linking at link time, such that the library executable code is included in the program. Dynamic linking is linking at run time; it involves building the program with information that supports run-time linking to a dynamic link library (DLL). For dynamic linking, a compatible DLL file must be available to the program at run time, but for static linking, the program is standalone.
Smart linking is performed by a build tool that excludes unused code in the linking process. For example, a program that only uses integers for arithmetic, or does no arithmetic operations at all, can exclude floating-point library routines. This can lead to smaller program file size and reduced memory usage.
A variant is a library containing compiled code (object code in IBM's nomenclature) in a form that cannot be loaded by the OS but that can be read by the linker.
A static library is sometimes called an archive on Unix-like systems.
The object library technology was developed since as OOP became popular, it became apparent that OOP runtime binding required information than contemporary libraries did not provide. In addition to the names and entry points of the code located within, due to inheritance, OOP binding also requires a list of dependencies since the full definition of a method may be in different places. Further, this requires more than listing that one library requires the services of another. In OOP, the libraries themselves may not be known at compile time, and vary from system to system.
The remote object technology was developed in parallel to support multi-tier programs with a user interface application running on a personal computer (PC) using services of a mainframe or minicomputer such as data storage and processing. For instance, a program on a PC would send messages to a minicomputer via remote procedure call (RPC) to retrieve relatively small samples from a relatively large dataset. In response, distributed object technology was developed.
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. For example, libfoo.so.2 might be version 2 of library foo and a link file named libfoo.so provides a version independent name to that file that programs link to. The link file could be changed to a refer to a version 3 (libfoo.so.3) such that consuming programs will then use version 3 without having to change the program.
Files with extension .la are libtool archives; not usable by the system.
A .ocx file can be either a static library or contain the information needed to build an application that consumes the associated DLL. In the latter case, the associated DLL file must be present at runtime.
target="_blank" rel="nofollow">[1]ftp://ftp.iecc.com/pub/linker/ Errata: [2]
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