Science Fair Project Encyclopedia
Source code (commonly just source or code) is any series of statements written in some human-readable computer programming language. In modern programming languages, the source code which constitutes a program is usually in several text files, but the same source code may be printed in a book or recorded on tape (usually without a filesystem). The term is typically used in the context of a particular piece of computer software. A computer program's source code is the collection of files that can be converted from human-readable form to an equivalent computer-executable form. The source code is either converted into executable by a compiler for a particular computer architecture, or executed from the human readable form with the aid of an interpreter.
Source code is either used to produce object code, or to be run by an interpreter. Modifications are not carried out on object code, but on source code, and then converted again.
Another important purpose of source code is for the description of software. Also, source code has a number of other uses. It can be used as a tool of learning; beginning programmers often find it helpful to review existing source code to learn about programming techniques and methodology. It is also used as a communication tool between experienced programmers, due to its (ideally) concise and unambiguous nature. The sharing of source code between developers is frequently cited as a contributing factor to the maturation of their programming skills. Source code can be an expressive artistic medium; consider, for example, obfuscated code or PerlMonks.Org.
Source code is a vital component in the activity of porting software to alternative computer platforms. Without the source code for a particular piece of software, portability is generally so difficult as to be impractical and even impossible. Programmers frequently borrow source code from one piece of software to use in other projects, a concept which is known as Software reusability.
The source code for a particular piece of software may be contained in a single file or many files. A program's source code is not necessarily all written in the same programming language; for example, it is common for a program to be written primarily in the C programming language, with some portions written in Assembly language for optimization purposes. It is also possible for some components of a piece of software to be written and compiled separately, in an arbitrary programming language, and later integrated into the software using a technique called library linking.
Moderately complex software customarily requires the compilation or assembly of several, sometimes dozens or even hundreds, of different source code files. This complexity is reduced considerably by the inclusion of a Makefile with the source code, which describes the relationships among the source code files, and contains information about how they are to be compiled. The revision control system is another tool frequently used by developers for source code maintenance.
Software, and its accompanying source code, typically falls within one of two licensing paradigms: Free software and Proprietary software. Generally speaking, software is free if the source code is freely available, and proprietary if the source code is kept secret, or is privately owned and restricted. The provisions of the various copyright laws are often used for this purpose, though trade secrecy is also relied upon. For a further discussion of the differences between these paradigms, and the divisions within them, see software license.
As of 2003, court systems are in the process of deciding whether source code should be considered a Constitutionally protected form of free speech in the United States. Proponents of the free speech argument claim that because source code conveys information to programmers, is written in a language, and can be used to share humour and other artistic pursuits, it is a protected form of communication. The opposing view is that source code is functional, more than artistic speech, and is thus not protected by First Amendment Rights of the U.S. Constitution.
One of the first court cases regarding the nature of source code as free speech involved University of California mathematics professor Dan Bernstein, who had published on the internet the source code for an encryption program that he created. At the time, encryption algorithms were classified as munitions by the United States government; exporting encryption to other countries was considered an issue of national security, and had to be approved by the State Department. The Electronic Frontier Foundation sued the U.S. government on Bernstein's behalf; the court ruled that source code was free speech, protected by the First Amendment.
In 2000, in a related court case, the issue was again brought under some scrutiny when the Motion Picture Association of America (MPAA) sued the 'hacker' magazine 2600 and a number of other websites for distributing the source code to DeCSS, an algorithm capable of decrypting scrambled DVD discs. The algorithm was developed to allow people to play legally purchased DVDs on the Linux operating system, which had no DVD software at the time. The US District court decision favored the MPAA; 2600 magazine was prohibited from posting or linking to the source code on their website. This ruling was widely considered a victory for the supporters of the Digital Millennium Copyright Act, as it established a legal precedent for the notion that source code is not Constitutionally protected free speech. It was affirmed by the Appeals Court and as of late 2003 is being appealed to the US Supreme Court.
To a computer, there is no real concept of "well-written" source code. However, to a human, the way a program is written can have some important consequences for the human maintainers. Many source code programming style guides, which stress readability and some language-specific conventions are aimed at the maintenance of the software source code, which involves debugging and updating. Other issues also come into considering whether code is well written, such as the logical structuring of the code into manageable sections. See Software quality.
- Programming language
- Legacy code
- Freedom of speech
- Source code repository
- Programming style
- Open source
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