In computer science, a library is a collection of subroutines used to develop software. Computer science (or computing science) is the study and the Science of the theoretical foundations of Information and Computation and their In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger Libraries contain code and data that provide services to independent programs. This allows code and data to be shared and changed in a modular fashion. Modular programming is a software design technique that increases the extent to which software is composed from separate parts called modules Some executables are both standalone programs and libraries, but most libraries are not executables. In Computing, an executable (file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a file that only contains Executables and libraries make references known as links to each other through the process known as linking, which is typically done by a linker.

Most modern operating systems (OS) provide libraries that implement the majority of system services. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination Such libraries have commoditized the services a modern application expects an OS to provide. Commodification (or commoditization) is the transformation of goods and services (or things that may not normally be regarded as goods or services into a Commodity As such, most code used by modern applications is provided in these libraries.

Contents 1 History 2 Types 2.1 Static libraries 2.2 Dynamic linking 2.2.1 Relocation 2.2.2 Locating libraries at runtime 2.2.3 Shared libraries 2.2.4 Dynamic loading 2.3 Remote libraries 2.4 Object Libraries 3 Naming 4 See also 5 References 6 External links

History

The earliest programming concepts analogous to libraries were intended to separate data definitions from the program implementation. Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's Implementation is the realization of an application or execution of a Plan, idea Model, Design, Specification, standard, Algorithm The COMPOOL (Communication Pool) concept was brought to popular attention by JOVIAL in 1959, although it borrowed the idea from the large-system SAGE software. The Semi-Automatic Ground Environment ( SAGE) was an automated control system for tracking and intercepting enemy Bomber aircraft used by NORAD from Following the computer science principles of Separation of Concerns and Information Hiding, "Comm Pool's purpose was to permit the sharing of System Data among many programs by providing a centralized data description. In Computer science, separation of concerns ( SoC) is the process of breaking a Computer program into distinct features that overlap in functionality as In Computer science, the principle of information hiding is the hiding of design decisions in a computer program that are most likely to change thus protecting " (Wexelblat 1981:369)

COBOL also included "primitive capabilities for a library system" in 1959 (Wexelblat 1981:274), but Jean Sammet described them as "inadequate library facilities" in retrospect. COBOL (ˈkoʊbɒl is one of the oldest programming languages still in active use Jean E Sammet (born 1928 is an American Computer scientist who developed the FORMAC programming language in 1962 (Wexelblat 1981:258)

Another major contributor to the modern library concept was the subprogram innovation of FORTRAN. In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger Fortran (previously FORTRAN) is a general-purpose, procedural, imperative Programming language that is especially suited to FORTRAN subprograms can be compiled independently of each other, but the compiler lacks a linker, so type checking between subprograms is impossible. In Computer science, a type system defines how a Programming language classifies values and expressions into '''types''', how it can (Wilson et al. 1988:126)

Finally, the influential Simula 67 cannot be overlooked. Simula is a name for two programming languages Simula I and Simula 67 developed in the 1960s at the Norwegian Computing Center in Oslo, by Ole-Johan Dahl Simula was the first object-oriented programming language, and its classes are nearly identical to the modern concept as used in Java, C++, and C#. Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs In Object-oriented programming, a class is a Programming language construct that is used as a blueprint to create objects This blueprint includes attributes C++ (" C Plus Plus " ˌsiːˌplʌsˈplʌs is a general-purpose Programming language. C# (pronounced C Sharp is a Multi-paradigm The class concept of Simula was also a progenitor of the package in Ada and the module of Modula-2. Ada is a structured, Statically typed, imperative, and object-oriented high-level computer Programming language Modula-2 is a computer Programming language invented by Niklaus Wirth at ETH, around 1978 as a successor to his intermediate language Modula (Wilson et al. 1988:52) Even when originally developed in 1965, Simula classes could be included in library files and added at compile time. (Wexelblat 1981:716)

Types

Static libraries

Main article: Static Library

Historically, libraries could only be static. In Computer science, a static library or statically-linked library is a set of routines external functions and variables which are resolved in a caller at Compile-time A static library, also known as an archive, consists of a set of routines which are copied into a target application by the compiler, linker, or binder, producing object files and a stand-alone executable file. In Computer science, a subroutine ( function, method, procedure, or subprogram) is a portion of code within a larger In Computer science, object code, or an object file, is the representation of code that a Compiler or Assembler generates by processing This process, and the stand-alone executable file, are known as a static build of the target application. A static build is a compiled version of a program which has been statically linked against libraries Actual addresses for jumps and other routine calls are stored in a relative or symbolic form which cannot be resolved until all code and libraries are assigned final static addresses.

The linker resolves all of the unresolved addresses into fixed or relocatable addresses (from a common base) by loading all code and libraries into actual runtime memory locations. This linking process can take as much, or more time than the compilation process, and must be performed when any of the modules is recompiled. Most compiled languages have a standard library (for example, the C standard library) but programmers can also create their own custom libraries. The C standard library (also known as libc) is a now-standardized collection of Header files and library routines used to implement common operations such Commercial compiler publishers provide both standard and custom libraries with their compiler products.

A linker may work on specific types of object files, and thus require specific (compatible) types of libraries. Collecting object files into a static library may ease their distribution and use. A client, either a program or a library subroutine, accesses a library object by referencing just its name. The linking process resolves references by searching the libraries in the order given. Usually, it is not considered an error if a name can be found multiple times in a given set of libraries.

Dynamic linking

Dynamic linking means that the subroutines of a library are loaded into an application program at runtime, rather than being linked in at compile time, and remain as separate files on disk. In Computer science, runtime or run time describes the operation of a Computer program, the duration of its execution from beginning to termination In Computer science, compile time refers to either the operations performed by a Compiler (the "compile-time operations" or Programming language A computer file is a block of Arbitrary Information, or resource for storing information which is available to a Computer program and is usually Disk storage is a general category of a Computer storage mechanisms in which data is recorded on planar round and rotating surfaces ( disks, discs, or Only a minimal amount of work is done at compile time by the linker; it only records what library routines the program needs and the index names or numbers of the routines in the library. The majority of the work of linking is done at the time the application is loaded (loadtime) or during execution (runtime). In Computing, a loader is the part of an operating system that is responsible for loading programs from executables (i The necessary linking code, called a loader, is actually part of the underlying operating system. In Computing, a loader is the part of an operating system that is responsible for loading programs from executables (i An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination At the appropriate time the loader finds the relevant libraries on disk and adds the relevant data from the libraries to the process's memory space. In computing a process is an instance of a Computer program that is being sequentially executed by a computer system that has the ability to run several computer

Some operating systems can only link in a library at loadtime, before the process starts executing; others may be able to wait until after the process has started to execute and link in the library just when it is actually referenced (i. e. , during runtime). In Computer science, runtime or run time describes the operation of a Computer program, the duration of its execution from beginning to termination The latter is often called "delay loading". In either case, such a library is called a dynamically linked library.

The nature of dynamic linking makes it a common boundary in software licenses. A software license (or software licence in commonwealth usage is a Legal instrument governing the usage or redistribution of copyright protected software

Plugins are one common usage of dynamically linked libraries, which is especially useful when the libraries can be replaced by other libraries with a similar interface, but different functionality. Software may be said to have a "plugin architecture" if it uses libraries for core functionality with the intention that they can be replaced. Note, however, that the use of dynamically linked libraries in an application's architecture does not necessarily mean that they may be replaced.

Dynamic linking was originally developed in the Multics operating system, starting in 1964. Multics ( Mult iplexed I nformation and C omputing S ervice was an extremely influential early Time-sharing Operating system It was also a feature of MTS (the Michigan Terminal System), built in the late 1960s. Michigan Terminal System ( MTS) is an Operating system for the IBM System/360 and its successors that was developed jointly by the following institutions ^[1] In Microsoft Windows, dynamically-linked libraries are called dynamic-link libraries or "DLLs". Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. Dynamic-link library (also written without the hyphen or DLL, is Microsoft 's implementation of the Shared library concept in the Microsoft Windows

Relocation

Main article: Relocation

One wrinkle that the loader must handle is that the actual location in memory of the library data cannot be known until after the executable and all dynamically linked libraries have been loaded into memory. This is because the memory locations used depend on which specific dynamic libraries have been loaded. It is not possible to depend on the absolute location of the data in the executable, nor even in the library, since conflicts between different libraries would result: if two of them specified the same or overlapping addresses, it would be impossible to use both in the same program.

However, in practice, the shared libraries on most systems do not change often. Therefore, it is possible to compute a likely load address for every shared library on the system before it is needed, and store that information in the libraries and executables. If every shared library that is loaded has undergone this process, then each will load at their predetermined addresses, which speeds up the process of dynamic linking. This optimization is known as prebinding in Mac OS X and prelinking in Linux. Prebinding is a method for reducing the time it takes to launch Executables in the Mach-O File format. prelink is a free program written by Jakub Jelinek of Red Hat for POSIX -compliant Operating systems principally Disadvantages of this technique include the time required to precompute these addresses every time the shared libraries change, the inability to use address space layout randomization, and the requirement of sufficient virtual address space for use (a problem that will be alleviated by the adoption of 64-bit architectures, at least for the time being). Address space layout randomization (ASLR is a computer security technique which involves randomly arranging the positions of key data areas usually including the base of the '64-bit' CPUs have existed in Supercomputers since the 1960s and in RISC -based workstations and servers since the early 1990s.

An old method was to examine the program at load time and replace all references to data in the libraries with pointers to the appropriate memory locations once all libraries have been loaded. On Windows 3.1 (and some embedded systems such as Texas Instruments calculators), the references to patch were arranged as linked lists, allowing easy enumeration and replacement. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints The TI-89 and the TI-89 Titanium are Graphing calculators developed by Texas Instruments. In Computer science, a linked list is one of the fundamental Data structures and can be used to implement other data structures Nowadays, most dynamic library systems link a symbol table with blank addresses into the program at compile time. In Computer science, a symbol table is a Data structure used by a language translator such as a Compiler or interpreter, where each Identifier All references to code or data in the library pass through this table, the import directory. At load time the table is modified with the location of the library code/data by the loader/linker. This process is still slow enough to significantly affect the speed of programs that call other programs at a very high rate, such as certain shell scripts. A shell script is a script written for the shell, or Command line interpreter, of an Operating system.

The library itself contains a jump table of all the methods within it, known as entry points. In Computer programming, a branch table (sometimes known as a jump table) is a term used to describe an efficient method of transferring program control ( branching Calls into the library "jump through" this table, looking up the location of the code in memory, then calling it. This introduces overhead in calling into the library, but the delay is usually so small as to be negligible.

Locating libraries at runtime

Main article: Dynamic linker

Dynamic linkers/loaders vary widely in functionality. In Computing, a dynamic linker is the part of an Operating system (OS that loads and links the Shared libraries for an executable when it is run Some depend on explicit paths to the libraries being stored in the executable. Any change to the library naming or layout of the filesystem will cause these systems to fail. More commonly, only the name of the library (and not the path) is stored in the executable, with the operating system supplying a system to find the library on-disk based on some algorithm.

Unix-like systems 

Most Unix-like systems have a "search path" specifying file system directories in which to look for dynamic libraries. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming In Computing, a directory, catalog, folder or drawer is an entity in a File system, which contains a group of files and/or other directories On some systems, the default path is specified in a configuration file; in others, it is hard coded into the dynamic loader. In Computing, configuration files, or config files', are used to configure the initial settings for some Computer programs They are used Some executable file formats can specify additional directories in which to search for libraries for a particular program. In Computing, an executable (file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a file that only contains This can usually be overridden with an environment variable, although it is disabled for setuid and setgid programs, so that a user can't force such a program to run arbitrary code. Environment variables are a set of dynamic values that can affect the way running processes will behave on a computer setuid and setgid (short for set u ser ID upon execution and set g roup ID upon execution respectively are Developers of libraries are encouraged to place their dynamic libraries in places in the default search path. On the downside, this can make installation of new libraries problematic, and these "known" locations quickly become home to an increasing number of library files, making management more complex.

Microsoft Windows 

Microsoft Windows will check the registry to determine the proper place to find an ActiveX DLL, but for other DLLs it will check the directory that the program was loaded from; the current working directory (only on older versions of Windows); any directories set by calling the SetDllDirectory() function; the System32, System, and Windows directories; and finally the directories specified by the PATH environment variable. The Windows registry is a directory which stores settings and options for the Operating system for Microsoft Windows 32-bit versions 64-bit versions and ActiveX is a Component object model (COM developed by Microsoft for Windows. Environment variables are a set of dynamic values that can affect the way running processes will behave on a computer ^[2] Applications written for the .NET Framework framework (since in 2002), also check the Global Assembly Cache as the primary store of shared dll files to remove the issue of DLL hell. The Global Assembly Cache or GAC is a machine-wide.NET assemblies Cache for Microsoft 's CLR platform. In Computing, DLL hell is a colloquial term for the complications that arise when working with dynamic link libraries, (DLLs used with Microsoft Windows

OpenStep 

OpenStep used a more flexible system, collecting a list of libraries from a number of known locations (similar to the PATH concept) when the system first starts. OpenStep is an Object-oriented Application programming interface (API specification for an Object-oriented operating system that uses any modern Operating Moving libraries around causes no problems at all, although there is a time cost when first starting the system.

AmigaOS 

Under AmigaOS generic system libraries are stored in a directory defined by the LIBS: path assignment and application-specific libraries can be stored in the same directory as the application's executable. AmigaOS is the default native Operating system of the Amiga personal computer AmigaOS will search these locations when an executable attempts to launch a shared library. An application may also supply an explicit path when attempting to launch a library.

One of the biggest disadvantages of dynamic linking is that the executables depend on the separately stored libraries in order to function properly. If the library is deleted, moved, or renamed, or if an incompatible version of the DLL is copied to a place that is earlier in the search, the executable could malfunction or even fail to load; damaging vital library files used by almost any executable in the system (such as the C library libc. The C standard library (also known as libc) is a now-standardized collection of Header files and library routines used to implement common operations such so on Unix systems) will usually render the system completely unusable. On Windows this is commonly known as DLL hell. In Computing, DLL hell is a colloquial term for the complications that arise when working with dynamic link libraries, (DLLs used with Microsoft Windows

Shared libraries

In addition to being loaded statically or dynamically, libraries are also often classified according to how they are shared among programs. Dynamic libraries almost always offer some form of sharing, allowing the same library to be used by multiple programs at the same time. Static libraries, by definition, cannot be shared. The term "linker" comes from the process of copying procedures or subroutines which may come from "relocatable" libraries and adjusting or "linking" the machine address to the final locations of each module.

The shared library term is slightly ambiguous, because it covers at least two different concepts. First, it is the sharing of code located on disk by unrelated programs. The second concept is the sharing of code in memory, when programs execute the same physical page of RAM, mapped into different address spaces. It would seem that the latter would be preferable, and indeed it has a number of advantages. For instance on the OpenStep system, applications were often only a few hundred kilobytes in size and loaded almost instantly; the vast majority of their code was located in libraries that had already been loaded for other purposes by the operating system. OpenStep is an Object-oriented Application programming interface (API specification for an Object-oriented operating system that uses any modern Operating There is a cost, however; shared code must be specifically written to run in a multitasking environment. In some older environments such as 16 bit Windows or MPE for the HP 3000, only stack based data (local) was allowed, or other significant restrictions were placed on writing a DLL.

RAM sharing can be accomplished by using position independent code as in Unix, which leads to a complex but flexible architecture, or by using position dependent code as in Windows and OS/2. In Computing, position-independent code ( PIC) or position-independent executable ( PIE) is machine instruction code that executes properly Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer OS/2 is a computer Operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively These systems make sure, by various tricks like pre-mapping the address space and reserving slots for each DLL, that code has a great probability of being shared. Windows DLLs are not shared libraries in the Unix sense. The rest of this section concentrates on aspects common to both variants.

In most modern operating systems, shared libraries can be of the same format as the "regular" executables. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination This allows two main advantages: first, it requires making only one loader for both of them, rather than two (having the single loader is considered well worth its added complexity). Secondly, it allows the executables also to be used as DLLs, if they have a symbol table. Typical executable/DLL formats are ELF and Mach-O (both in Unix) and PE (Windows). In Computing, the Executable and Linking Format ( ELF, formerly called Extensible Linking Format) is a common standard File format for Executables Mach-O, short for Mach object file format is a File format for Executables Object code, Shared libraries, dynamically-loaded The Portable Executable (PE format is a File format for Executables object code, and DLLs used in 32-bit and 64-bit versions of Windows In Windows, the concept was taken one step further, with even system resources such as fonts being bundled in the DLL file format. The same is true under OpenStep, where the universal "bundle" format is used for almost all system resources.

The term DLL is mostly used on Windows and OS/2 products. OS/2 is a computer Operating system, initially created by Microsoft and IBM, then later developed by IBM exclusively On Unix and Unix-like platforms, the term shared library or shared object is more commonly used; consequently, the most common filename extension for shared library files is . A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming A filename extension is a suffix to the name of a Computer file applied to indicate the encoding convention ( File format) of its contents so, usually followed by another dot and a version number. This is technically justified in view of the different semantics. More explanations are available in the position independent code article. In Computing, position-independent code ( PIC) or position-independent executable ( PIE) is machine instruction code that executes properly

In some cases, an operating system can become overloaded with different versions of DLLs, which impedes its performance and stability. Such a scenario is known as DLL hell. In Computing, DLL hell is a colloquial term for the complications that arise when working with dynamic link libraries, (DLLs used with Microsoft Windows Most modern operating systems, after 2001, have clean-up methods to eliminate such situations.

Dynamic loading

Main article: Dynamic loading

Dynamic loading is a subset of dynamic linking where a dynamically linked library loads and unloads at run-time on request. Dynamic loading is a mechanism by which a Computer program can at Runtime, load a library (or other binary) into memory retrieve the addresses In Computer science, runtime or run time describes the operation of a Computer program, the duration of its execution from beginning to termination Such a request may be made implicitly at compile-time or explicitly at run-time. In Computer science, compile time refers to either the operations performed by a Compiler (the "compile-time operations" or Programming language In Computer science, runtime or run time describes the operation of a Computer program, the duration of its execution from beginning to termination Implicit requests are made at compile-time when a linker adds library references that include file paths or simply file names. Explicit requests are made when applications make direct calls to an operating system's API at runtime.

Most operating systems that support dynamically linked libraries also support dynamically loading such libraries via a run-time linker API. In Computer science, runtime or run time describes the operation of a Computer program, the duration of its execution from beginning to termination For instance, Microsoft Windows uses the API functions LoadLibrary, LoadLibraryEx, FreeLibrary and GetProcAddress with Microsoft Dynamic Link Libraries; POSIX based systems, including most UNIX and UNIX-like systems, use dlopen, dlclose and dlsym. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. Dynamic-link library (also written without the hyphen or DLL, is Microsoft 's implementation of the Shared library concept in the Microsoft Windows POSIX (ˈpɒzɪks or "Portable Operating System Interface" is the collective name of a family of related standards specified by the IEEE to define Some development systems automate this process.

Remote libraries

Another solution to the library issue is to use completely separate executables (often in some lightweight form) and call them using a remote procedure call (RPC) over a network to another computer. Remote procedure call ( RPC) is an Inter-process communication technology that allows a Computer program to cause a Subroutine or procedure to This approach maximizes operating system re-use: the code needed to support the library is the same code being used to provide application support and security for every other program. Additionally, such systems do not require the library to exist on the same machine, but can forward the requests over the network.

The downside to such an approach is that every library call requires a considerable amount of overhead. RPC calls are much more expensive than calling a shared library which has already been loaded on the same machine. This approach is commonly used in a distributed architecture which makes heavy use of such remote calls, notably client-server systems and application servers such as Enterprise JavaBeans. In n-tier architecture an application server is a Server that hosts an API to expose Business Logic and Business Processes for use by other Enterprise JavaBeans&trade ( EJB) is a managed server-side component architecture for modular construction of enterprise applications

Object Libraries

Although dynamic linking was originally developed in the 1960s, it did not reach consumer operating systems until the late 1980s; it was generally available in some form in most operating systems by the early 1990s. It was during this same period that object-oriented programming (OOP) was becoming a significant part of the programming landscape. Object-oriented programming (OOP is a Programming paradigm that uses " objects " and their interactions to design applications and computer programs OOP with runtime binding requires additional information that traditional libraries don't supply; in addition to the names and entry points of the code located within, they also require a list of the objects on which they depend. This is a side-effect of one of OOP's main advantages, inheritance, which means that the complete definition of any method may be defined in a number of places. This is more than simply listing that one library requires the services of another; in a true OOP system, the libraries themselves may not be known at compile time, and vary from system to system. In Computer science, compile time refers to either the operations performed by a Compiler (the "compile-time operations" or Programming language

At the same time another common area for development was the idea of multi-tier programs, in which a "display" running on a desktop computer would use the services of a mainframe or minicomputer for data storage or processing. Mainframes (often colloquially referred to as Big Iron) are Computers used mainly by large organizations for critical applications typically bulk data A minicomputer (colloquially mini) is a class of multi-user Computers that lies in the middle range of the computing spectrum in between the largest Multi-user For instance, a program on a GUI-based computer would send messages to a minicomputer to return small samples of a huge dataset for display. Remote procedure calls already handled these tasks, but there was no standard RPC system. Remote procedure call ( RPC) is an Inter-process communication technology that allows a Computer program to cause a Subroutine or procedure to

It was not long before the majority of the minicomputer and mainframe vendors were working on projects to combine the two, producing an OOP library format that could be used anywhere. Such systems were known as object libraries, or distributed objects if they supported remote access (not all did). Microsoft's COM is an example of such a system for local use, DCOM a modified version that support remote access.

For some time object libraries were the "next big thing" in the programming world. There were a number of efforts to create systems that would run across platforms, and companies competed to try to get developers locked into their own system. Examples include IBM's System Object Model (SOM/DSOM), Sun Microsystems' Distributed Objects Everywhere (DOE), NeXT's Portable Distributed Objects (PDO), Digital's ObjectBroker, Microsoft's Component Object Model (COM/DCOM), and any number of CORBA-based systems. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology For the similarly-named executable file format in the HP-UX operating system see System Object Model (file format In computing the System Object Sun Microsystems Inc ( is a multinational vendor of Computers computer components Computer software, and Information technology services Distributed Objects Everywhere ( DOE) was a long-running Sun Microsystems project to build a Distributed computing environment based on the CORBA NeXT Computer Inc (later NeXT Software Inc) was an American Computer company headquartered in Redwood City, California that Portable Distributed Objects, or PDO, is a Programming API for creating Object-oriented code that can be executed remotely on a network A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for ObjectBroker is A distributed object system from DEC based on the CORBA standard Component Object Model ( COM) is an interface standard for Software componentry introduced by Microsoft in 1993 The Common Object Requesting Broker Architecture (CORBA is a standard defined by the Object Management Group (OMG that enables software components written

In the end, it turned out that OOP libraries were not the next big thing. With the exception of Microsoft's COM and NeXT's (now Apple Computer) PDO, all of these efforts have since ended. Apple Inc, ( formerly Apple Computer Inc, is an American Multinational corporation with a focus on designing and manufacturing Consumer electronics

The JAR file format is mainly used for object libraries in the Java programming language. In Computing, a JAR file (or J ava AR chive is used for aggregating many files into one It consists of (sometimes compressed) classes in bytecode format and is loaded by a java virtual machine or special class loaders.

Naming

GNU/Linux, Solaris and other System V Release 4 derivatives, and BSD variants

libfoo. GNU ( pronounced) is a computer Operating system composed entirely of Free software. Linux (commonly pronounced ˈlɪnəks Solaris is a Unix -based Operating system introduced by Sun Microsystems in 1992 as the successor to SunOS. Unix System V, commonly abbreviated SysV (and usually pronounced though rarely written as System 5 was one of the versions of the Unix Operating system a and libfoo. so files are placed in directories like /lib, /usr/lib or /usr/local/lib. The filenames always start with lib, and end with . a (archive, static library) or . so (shared object, dynamically linked library), with an optional interface number. For example libfoo. so. 2 is the second major interface revision of the dynamically linked library libfoo. Old Unix versions would use major and minor library revision numbers (libfoo. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer so. 1. 2) while contemporary Unixes will only use major revision numbers (libfoo. so. 1). Dynamically loaded libraries are placed in /usr/libexec and similar directories. The . la files sometimes found in the library directories are libtool archives, not usable by the system as such. GNU Libtool is a GNU Programming tool from the GNU build system used for creating portable software libraries.

Mac OS X and upwards

The system inherits static library conventions from BSD, with the library being in a . Mac OS X (mæk oʊ ɛs tɛn is a line of computer Operating systems developed marketed and sold by Apple Inc, the latest of which is pre-loaded on all currently a file, and can use . so-style dynamically-linked libraries (with the . dylib suffix instead). Most libraries in Mac OS X, however, are "frameworks", placed inside of special directories called "bundles", which wrap the library's required files and metadata. Under NEXTSTEP, Mac OS X and GNUstep, a bundle is a directory that allows related resources such as Software code to be For example a library called "My Neat Library" would be implemented in a bundle called "My Neat Library. framework".

Microsoft Windows

*. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. DLL files are dynamically linkable libraries. Dynamic-link library (also written without the hyphen or DLL, is Microsoft 's implementation of the Shared library concept in the Microsoft Windows Dynamic-link library (also written without the hyphen or DLL, is Microsoft 's implementation of the Shared library concept in the Microsoft Windows Other file name patterns may be used for specific purpose DLLs, e. g. *. OCX for OCX control libraries. Object Linking and Embedding ( OLE) is a technology that allows embedding and linking to documents and other objects developed by Microsoft. The interface revisions are either encoded in the files, or abstracted away using COM-object interfaces. Component Object Model ( COM) is an interface standard for Software componentry introduced by Microsoft in 1993 Depending on how they are compiled, *. LIB files can be either static libraries or representations of dynamically linkable libraries needed only during compilation, known as "Import Libraries". Unlike in the UNIX world, where different file extensions are used, when linking against . Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer LIB file in Windows one must first know if it is a regular static library or an import library. Microsoft Windows is a series of Software Operating systems and Graphical user interfaces produced by Microsoft. In the latter case, a . DLL file must be present at runtime. Dynamic-link library (also written without the hyphen or DLL, is Microsoft 's implementation of the Shared library concept in the Microsoft Windows

See also

• Code reuse
• Linker
• Loader (computing)
• Microsoft Dynamic Link Library
• Object file
• Plugin
• Prebinding
• Static library
• Runtime library
• C standard library
• Java Class Library
• Base Class Library

References

• Wexelblat, Richard (1981), History of Programming Languages, ACM Monograph Series, New York, NY: Academic Press (A subsidiary of Harcourt Brace), ISBN 0-12-745040-8 </ref>
• Wilson, L. Harcourt Trade Publishers is a US Publishing firm with a long history of publishing fiction and nonfiction for children and adults B. & Clark, R. G. (1988), Comparative Programming Languages, Wokingham, England: Addison-Wesley, ISBN 0-201-18483-4 

External links

• Program Library HOWTO for Linux
• Shared Libraries - 'Linkers and Loaders' by John R. Levine
• Dynamic Linking and Loading - 'Linkers and Loaders' by John R. Levine
• Article Faster C++ program startups by improving runtime linking efficiency by Léon Bottou and John Ryland
• How to Create Program Libraries by Baris Simsek
• LIB BFD - the Binary File Descriptor Library
• 1st Library-Centric Software Design Workshop LCSD'05 at OOPSLA'05
• 2nd Library-Centric Software Design Workshop LCSD'06 at OOPSLA'06
• How to create shared library(with much background info)

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