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In computer science, a library is a collection of non-volatile resources used by computer programs, often to develop software. These may include configuration data, documentation, help data, message templates, pre-written code and subroutines, classes, values or type specifications. In IBM's OS/360 and its successors they are referred to as partitioned data sets. In computer science, a library is a collection of implementations of behavior, written in terms of a language, that has a well-defined interface by which the behavior is invoked. This means that as long as a higher level program uses a library to make system calls, it does not need to be re-written to implement those system calls over and over again. In addition, the behavior is provided for reuse by multiple independent programs. A program invokes the library-provided behavior via a mechanism of the language. For example, in a simple imperative language such as C, the behavior in a library is invoked by using C's normal function-call. What distinguishes the call as being to a library, versus being to another function in the same program, is the way that the code is organized in the system. Library code is organized in such a way that it can be used by multiple programs that have no connection to each other, while code that is part of a program is organized to only be used within that one program. This distinction can gain a hierarchical notion when a program grows large, such as a multi-million-line program. In that case, there may be internal libraries that are reused by independent sub-portions of the large program. The distinguishing feature is that a library is organized for the purposes of being reused by independent programs or sub-programs, and the user only needs to know the interface, and not the internal details of the library. The value of a library is the reuse of the behavior. When a program invokes a library, it gains the behavior implemented inside that library without having to implement that behavior itself. Libraries encourage the sharing of code in a modular fashion, and ease the distribution of the code. The behavior implemented by a library can be connected to the invoking program at different program lifecycle phases. If the code of the library is accessed during the build of the invoking program, then the library is called a static library. An alternative is to build the executable of the invoking program and distribute that, independently from the library implementation. The library behavior is connected after the executable has been invoked to be executed, either as part of the process of starting the execution, or in the middle of execution. In this case the library is called a dynamic library. A dynamic library can be loaded and linked as part of preparing a program for execution, by the linker. Alternatively, in the middle of execution, an application may explicitly request that a module be loaded. Most compiled languages have a standard library although programmers can also create their own custom libraries. Most modern software systems provide libraries that implement the majority of system services. Such libraries have commoditized the services which a modern application requires. As such, most code used by modern applications is provided in these system libraries. ==History== The earliest programming concepts analogous to libraries were intended to separate data definitions from the program implementation. JOVIAL brought the "COMPOOL" (Communication Pool) concept to popular attention in 1959, although it adopted the idea from the large-system SAGE software. 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." COBOL also included "primitive capabilities for a library system" in 1959,〔Wexelblat, ''op. cit.'', p. 274〕 but Jean Sammet described them as "inadequate library facilities" in retrospect.〔Wexelblat, ''op. cit.'', p. 258〕 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 lacks a linker. So prior to the introduction of modules in Fortran-90, type checking between FORTRAN〔It was possible earlier between, e.g., Ada subprograms.〕 subprograms was impossible. Finally, historians of the concept should remember the influential Simula 67. 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#. The ''class'' concept of Simula was also a progenitor of the ''package'' in Ada and the ''module'' of Modula-2.〔Wilson and Clark, ''op. cit.'', p. 52〕 Even when developed originally in 1965, Simula classes could be included in library files and added at compile time.〔Wexelblat, ''op. cit.'', p. 716〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Library (computing)」の詳細全文を読む スポンサード リンク
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