Source code - AbsoluteAstronomy.com

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, source code is text written using the format and syntax of the programming language

Programming language

A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

that it is being written in. Such a language is specially designed to facilitate the work of computer programmer

Programmer

A programmer, computer programmer or coder is someone who writes computer software. The term computer programmer can refer to a specialist in one area of computer programming or to a generalist who writes code for many kinds of software. One who practices or professes a formal approach to...

s, who specify the actions to be performed by a computer mostly by writing source code, which can then be automatically translated to binary machine code

Machine code

Machine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data Machine code or machine language is a system of impartible instructions...

that the computer can directly read and execute.
An interpreter

Interpreter (computing)

In computer science, an interpreter normally means a computer program that executes, i.e. performs, instructions written in a programming language...

translates to machine code and executes it on the fly

On the fly

-Colloquial usage:In colloquial use, on the fly means something created when needed. The phrase is used to mean:# something that was not planned ahead# changes that are made during the execution of same activity: ex tempore, impromptu.-Automotive usage:...

, while a compiler

Compiler

A compiler is a computer program that transforms source code written in a programming language into another computer language...

only translates to machine code that it stores as executable

Executable

In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU...

files; these can then be executed as a separate step.

Most computer applications are distributed in a form that includes executable files, but not their source code, which is useful to a user, programmer, or system administrator

System administrator

A system administrator, IT systems administrator, systems administrator, or sysadmin is a person employed to maintain and operate a computer system and/or network...

who wishes to modify the program or understand how it works.

The source code which constitutes a program

Computer program

A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

is usually held in one or more text file

Text file

A text file is a kind of computer file that is structured as a sequence of lines of electronic text. A text file exists within a computer file system...

s stored on a computer's hard disk

Hard disk

A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...

; usually these files are carefully arranged into a directory tree

Directory (file systems)

In computing, a folder, directory, catalog, or drawer, is a virtual container originally derived from an earlier Object-oriented programming concept by the same name within a digital file system, in which groups of computer files and other folders can be kept and organized.A typical file system may...

, known as a source tree. Source code can also be stored in a database (as is common for stored procedure

Stored procedure

A stored procedure is a subroutine available to applications that access a relational database system. A stored procedure is actually stored in the database data dictionary.Typical uses for stored procedures include data validation or access control mechanisms...

s) or elsewhere.

Source code also appears in books and other media; often in the form of small code snippets, but occasionally complete code bases; a well-known case is the source code of PGP

Pretty Good Privacy

Pretty Good Privacy is a data encryption and decryption computer program that provides cryptographic privacy and authentication for data communication. PGP is often used for signing, encrypting and decrypting texts, E-mails, files, directories and whole disk partitions to increase the security...

.

The notion of source code may also be taken more broadly, to include machine code and notations in graphical languages, neither of which are textual in nature. An example from an article presented on the annual IEEE conference on Source Code Analysis and Manipulation:

For the purpose of clarity ‘source code’ is taken to mean any fully executable description of a software system. It is therefore so construed as to include machine code, very high level languages and executable graphical representations of systems.

The code base of a programming project is the larger collection of all the source code of all the computer program

Computer program

s which make up the project.

It has become common practice to maintain code bases in version control systems.

Organization

The source code for a particular piece of software may be contained in a single file or many files. Though the practice is uncommon, a program's source code can be written in different programming languages. For example, a program written primarily in the C programming language

C (programming language)

C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

, might have portions written in assembly language

Assembly language

An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...

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. This is the case in some languages, such as Java

Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...

: each class is compiled separately into a file and linked by the interpreter at runtime.

Yet another method is to make the main program an interpreter for a programming language, either designed specifically for the application in question or general-purpose, and then write the bulk of the actual user functionality as macros or other forms of add-ins in this language, an approach taken for example by the GNU Emacs text editor.

Moderately complex software customarily requires the compilation or assembly of several, sometimes dozens or even hundreds, of different source code files. In these cases, instructions for compilations, such as a Makefile, are included with the source code. These describe the relationships among the source code files, and contain information about how they are to be compiled.

The revision control

Revision control

Revision control, also known as version control and source control , is the management of changes to documents, programs, and other information stored as computer files. It is most commonly used in software development, where a team of people may change the same files...

system is another tool frequently used by developers for source code maintenance.

Purposes

Source code is primarily used as input to the process that produces an executable program (i.e., it is compiled

Compiler

A compiler is a computer program that transforms source code written in a programming language into another computer language...

or interpreted

Interpreter (computing)

In computer science, an interpreter normally means a computer program that executes, i.e. performs, instructions written in a programming language...

). It is also used as a method of communicating algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

s between people (e.g., code snippets in books).

Programmers often find it helpful to review existing source code to learn about programming techniques. The sharing of source code between developers is frequently cited as a contributing factor to the maturation of their programming skills. Some people consider source code an expressive artistic medium

Media (arts)

In the arts, a media or medium is a material used by an artist or designer to create a work.-Architecture:In the art and science of architecture, the design and construction of buildings and interiors, infrastructure and other physical structures are created...

.

Porting

Porting

In computer science, porting is the process of adapting software so that an executable program can be created for a computing environment that is different from the one for which it was originally designed...

software to other computer platforms is usually prohibitively difficult without source code. Without the source code for a particular piece of software, portability is generally computationally expensive. Possible porting options include binary translation

Binary translation

In computing, binary translation is the emulation of one instruction set by another through translation of code. Sequences of instructions are translated from the source to the target instruction set...

and emulation of the original platform.

Decompilation of an executable program can be used to generate source code, either in assembly code or in a high level language.

Programmers frequently adapt source code from one piece of software to use in other projects, a concept known as software reusability.

Licensing

Software, and its accompanying source code, typically falls within one of two licensing paradigms: free software

Free software

Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

and proprietary software

Proprietary software

Proprietary software is computer software licensed under exclusive legal right of the copyright holder. The licensee is given the right to use the software under certain conditions, while restricted from other uses, such as modification, further distribution, or reverse engineering.Complementary...

.

Generally speaking, software is free if the source code is free to use, distribute, modify and study, and proprietary if the source code is kept secret, or is privately owned and restricted. Note that "free" refers to freedom, not price. Under many licenses it is acceptable to charge for "free software". The first free software license to be published and to explicitly grant these freedoms was the GNU General Public License

GNU General Public License

The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....

in 1989. The GNU GPL was originally intended to be used with the GNU operating system. The GNU GPL was later adopted by other non-GNU software projects such as the Linux kernel

Linux kernel

The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....

.

For proprietary software, the provisions of the various copyright laws, trade secrecy

Trade secret

A trade secret is a formula, practice, process, design, instrument, pattern, or compilation of information which is not generally known or reasonably ascertainable, by which a business can obtain an economic advantage over competitors or customers...

and patent

Patent

A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

s are used to keep the source code closed. Additionally, many pieces of retail software

Retail software

Retail software is computer software sold to end consumers, usually under restricted licenses. Until the emergence of the Internet, retail software represented, until the 2000s, the vast majority of all end consumer software used and was referred to as shrinkware because software almost always...

come with an end-user license agreement

Software license agreement

A software license agreement is a contract between the "licensor" and purchaser of the right to use software. The license may define ways under which the copy can be used, in addition to the automatic rights of the buyer including the first sale doctrine and .Many form contracts are only contained...

(EULA) which typically prohibits decompilation, reverse engineering

Reverse engineering

Reverse engineering is the process of discovering the technological principles of a device, object, or system through analysis of its structure, function, and operation...

, analysis, modification, or circumventing of copy protection

Copy protection

Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...

. Types of source code protection — beyond traditional compilation

Compiler

A compiler is a computer program that transforms source code written in a programming language into another computer language...

to object code

Object code

Object code, or sometimes object module, is what a computer compiler produces. In a general sense object code is a sequence of statements in a computer language, usually a machine code language....

— include code encryption, code obfuscation or code morphing

Code morphing

Code morphing is one of the approaches to protect software applications from reverse engineering, analysis, modifications, and cracking used in obfuscating software. This technology protects intermediate level code such as compiled from Java and .NET languages rather than binary object code...

Legal issues in the United States

In a 2003 court case in the United States, it was ruled that source code should be considered a constitutionally protected form of free speech. Proponents of free speech argued 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.

One of the first court cases regarding the nature of source code as free speech involved University of California

University of California

The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...

mathematics

Mathematics

Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...

professor Dan Bernstein, who had published on the internet the source code for an encryption

Encryption

In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...

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

National security

National security is the requirement to maintain the survival of the state through the use of economic, diplomacy, power projection and political power. The concept developed mostly in the United States of America after World War II...

, and had to be approved by the State Department

United States Department of State

The United States Department of State , is the United States federal executive department responsible for international relations of the United States, equivalent to the foreign ministries of other countries...

. The Electronic Frontier Foundation

Electronic Frontier Foundation

The Electronic Frontier Foundation is an international non-profit digital rights advocacy and legal organization based in the United States...

sued the U.S. government

Federal government of the United States

The federal government of the United States is the national government of the constitutional republic of fifty states that is the United States of America. The federal government comprises three distinct branches of government: a legislative, an executive and a judiciary. These branches and...

on Bernstein's behalf; the court ruled that source code was free speech, protected by the First Amendment.

Quality

The way a program is written can have important consequences for its maintainers. Coding conventions

Coding conventions

Coding conventions are a set of guidelines for a specific programming language that recommend programming style, practices and methods for each aspect of a piece program written in this language...

, which stress readability and some language-specific conventions, are aimed at the maintenance of the software source code, which involves debugging and updating. Other priorities, such as the speed of the program's execution, or the ability to compile the program for multiple architectures, often make code readability a less important consideration, since code quality depends entirely on its purpose.

External links

Source Code Definition - by The Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

Information Project (LINFO)
Google public source code search
Same program written in multiple languages

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Organization

Purposes

Licensing

Legal issues in the United States

Quality

See also

External links