Source code

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Simple C-language source code example, a procedural programming language. The resulting program prints "hello, world" on the computer screen. This first known "Hello world" snippet from the seminal book The C Programming Language originates from Brian Kernighan in the Bell Laboratories in 1974. Hello world c.svg
Simple C-language source code example, a procedural programming language. The resulting program prints "hello, world" on the computer screen. This first known "Hello world" snippet from the seminal book The C Programming Language originates from Brian Kernighan in the Bell Laboratories in 1974.

In computing, source code, or simply code, is any collection of text, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source code.

Contents

The source code is often transformed by an assembler or compiler into binary machine code that can be executed by the computer. The machine code is then available for execution at a later time.

Most application software is distributed in a form that includes only executable files. If the source code were included it would be useful to a user, programmer or a system administrator, any of whom might wish to study or modify the program.

Alternatively, depending on the technology being used, source code may be interpreted and executed directly.

Definitions


Richard Stallman's definition, formulated in his 1989 seminal license, proposed source code as whatever form in which software is modified:

The “source code” for a work means the preferred form of the work for making modifications to it. [2]


Some classical sources define source code as the text form of programming languages, for example:

Source code (also referred to as source or code) is the version of software as it is originally written (i.e., typed into a computer) by a human in plain text (i.e., human readable alphanumeric characters). [3]

This responds to the fact that, when program translation first appeared, the contemporary form of software production were textual programming languages, thus source code was text code while machine code was target code. However, as programming pipelines started to incorporate more intermediate forms, some in languages like JavaScript that could be either source or target, text code stopped being synonymous with source code.

Stallman's definition thus contemplates JavaScript and HTML's source-target ambivalence, as well as contemplating possible future forms of software production, like visual programming languages, or datasets in Machine Learning. [4] [5]

Other broader interpretations, however, consider source code to include the machine code along with all the high level languages that produce it, this definition undoes the original machine/text distinction by considering each step in the program translation to be source code.

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. [6] [7]

This approach allows for a much more flexible approach to system analysis, dispensing with the requirement for designer to collaborate by publishing a convenient form for understanding and modification. It can also be applied to scenarios where a designer is not needed, like DNA. However, this form of analysis doesn't contemplate a costlier machine-to-machine code analysis than human-to-machine code analysis.

History

The earliest programs for stored-program computers were entered in binary through the front panel switches of the computer. This first-generation programming language had no distinction between source code and machine code.

When IBM first offered software to work with its machine, the source code was provided at no additional charge. At that time, the cost of developing and supporting software was included in the price of the hardware. For decades, IBM distributed source code with its software product licenses, until 1983. [8]

Most early computer magazines published source code as type-in programs.

Occasionally the entire source code to a large program is published as a hardback book, such as Computers and Typesetting, vol. B: TeX, The Program by Donald Knuth, PGP Source Code and Internals by Philip Zimmermann, PC SpeedScript by Randy Thompson, and µC/OS, The Real-Time Kernel by Jean Labrosse.

Organization

The source code which constitutes a program is usually held in one or more text files stored on a computer's hard disk; usually, these files are carefully arranged into a directory tree, known as a source tree. Source code can also be stored in a database (as is common for stored procedures) or elsewhere.

A more complex Java source code example. Written in object-oriented programming style, it demonstrates boilerplate code. With prologue comments indicated in red, inline comments indicated in green, and program statements indicated in blue. CodeCmmt002.svg
A more complex Java source code example. Written in object-oriented programming style, it demonstrates boilerplate code. With prologue comments indicated in red, inline comments indicated in green, and program statements indicated in blue.

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. [9] For example, a program written primarily in the C programming language, might have 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. In some languages, such as Java, this can be done at runtime (each class is compiled into a separate file that is linked by the interpreter at runtime).

Yet another method is to make the main program an interpreter for a programming language, [10] 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.

The code base of a computer programming project is the larger collection of all the source code of all the computer programs which make up the project. It has become common practice to maintain code bases in version control systems. Moderately complex software customarily requires the compilation or assembly of several, sometimes dozens or maybe 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 programming relationships among the source code files and contain information about how they are to be compiled.

Purposes

Source code is primarily used as input to the process that produces an executable program (i.e., it is compiled or interpreted). It is also used as a method of communicating algorithms between people (e.g., code snippets in books). [11]

Computer programmers often find it helpful to review existing source code to learn about programming techniques. [11] The sharing of source code between developers is frequently cited as a contributing factor to the maturation of their programming skills. [11] Some people consider source code an expressive artistic medium. [12]

Porting 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. [13] Possible porting options include binary translation 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.

The situation varies worldwide, but in the United States before 1974, software and its source code was not copyrightable and therefore always public domain software. [14]

In 1974, the US Commission on New Technological Uses of Copyrighted Works (CONTU) decided that "computer programs, to the extent that they embody an author's original creation, are proper subject matter of copyright". [15] [16]

In 1983 in the United States court case Apple v. Franklin it was ruled that the same applied to object code; and that the Copyright Act gave computer programs the copyright status of literary works.

In 1999, in the United States court case Bernstein v. United States it was further ruled that source code could 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 humor and other artistic pursuits, it is a protected form of communication. [17] [18] [19]

Licensing

Copyright notice example: [20]

Copyright [yyyy] [name of copyright owner]

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

An author of a non-trivial work like software, [16] has several exclusive rights, among them the copyright for the source code and object code. [21] The author has the right and possibility to grant customers and users of his software some of his exclusive rights in form of software licensing. Software, and its accompanying source code, can be associated with several licensing paradigms; the most important distinction is free software vs proprietary software. This is done by including a copyright notice that declares licensing terms. If no notice is found, then the default of All rights reserved is implied.

Generally speaking, a software is free software if its users are free to use it for any purpose, study and change its source code, give or sell its exact copies, and give or sell its modified copies. Software is proprietary if it is distributed while the source code is kept secret, or is privately owned and restricted. One of the first software licenses to be published and to explicitly grant these freedoms was the GNU General Public License in 1989; the BSD license is another early example from 1990.

For proprietary software, the provisions of the various copyright laws, trade secrecy and patents are used to keep the source code closed. Additionally, many pieces of retail software come with an end-user license agreement (EULA) which typically prohibits decompilation, reverse engineering, analysis, modification, or circumventing of copy protection. Types of source code protection—beyond traditional compilation to object code—include code encryption, code obfuscation or code morphing.

Quality

The way a program is written can have important consequences for its maintainers. Coding conventions, 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 generally depends on its purpose.

See also

Related Research Articles

Computer programming is the process of performing a particular computation, usually by designing and building an executable computer program. Programming involves tasks such as analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms. The source code of a program is written in one or more languages that are intelligible to programmers, rather than machine code, which is directly executed by the central processing unit. The purpose of programming is to find a sequence of instructions that will automate the performance of a task on a computer, often for solving a given problem. Proficient programming thus usually requires expertise in several different subjects, including knowledge of the application domain, specialized algorithms, and formal logic.

<span class="mw-page-title-main">Free software</span> Software licensed to preserve user freedoms

Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, not price; all users are legally free to do what they want with their copies of a free software regardless of how much is paid to obtain the program. Computer programs are deemed "free" if they give end-users ultimate control over the software and, subsequently, over their devices.

<span class="mw-page-title-main">GNU</span> Free software collection

GNU is an extensive collection of free software, which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operating systems popularly known as Linux. Most of GNU is licensed under the GNU Project's own General Public License (GPL).

<span class="mw-page-title-main">GNU Compiler Collection</span> Free and open-source compiler for various programming languages

The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free software under the GNU General Public License. GCC is a key component of the GNU toolchain and the standard compiler for most projects related to GNU and the Linux kernel. With roughly 15 million lines of code in 2019, GCC is one of the biggest free programs in existence. It has played an important role in the growth of free software, as both a tool and an example.

<span class="mw-page-title-main">GNU Debugger</span> Source-level debugger

The GNU Debugger (GDB) is a portable debugger that runs on many Unix-like systems and works for many programming languages, including Ada, C, C++, Objective-C, Free Pascal, Fortran, Go, and partially others.

<span class="mw-page-title-main">Open-source license</span> Software license allowing source code to be used, modified, and shared

Open-source licenses facilitate free and open-source software (FOSS) development. Intellectual property (IP) laws restrict the modification and sharing of creative works. Free and open-source software licenses use these existing legal structures for the inverse purpose of granting freedoms that promote sharing and collaboration. They grant the recipient the rights to use the software, examine the source code, modify it, and distribute the modifications. These licenses target computer software where source code can be necessary to create modifications. They also cover situations where there is no difference between the source code and the executable program distributed to end users. Open-source licenses can cover hardware, infrastructure, drinks, books, and music.

Gosling Emacs is a discontinued Emacs implementation written in 1981 by James Gosling in C.

<span class="mw-page-title-main">GNU Project</span> Free software project

The GNU Project is a free software, mass collaboration project announced by Richard Stallman on September 27, 1983. Its goal is to give computer users freedom and control in their use of their computers and computing devices by collaboratively developing and publishing software that gives everyone the rights to freely run the software, copy and distribute it, study it, and modify it. GNU software grants these rights in its license.

<span class="mw-page-title-main">Open-source software</span> Software licensed to ensure source code usage rights

Open-source software (OSS) is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose. Open-source software may be developed in a collaborative public manner. Open-source software is a prominent example of open collaboration, meaning any capable user is able to participate online in development, making the number of possible contributors indefinite. The ability to examine the code facilitates public trust in the software.

A programming tool or software development tool is a computer program that software developers use to create, debug, maintain, or otherwise support other programs and applications. The term usually refers to relatively simple programs, that can be combined to accomplish a task, much as one might use multiple hands to fix a physical object. The most basic tools are a source code editor and a compiler or interpreter, which are used ubiquitously and continuously. Other tools are used more or less depending on the language, development methodology, and individual engineer, often used for a discrete task, like a debugger or profiler. Tools may be discrete programs, executed separately – often from the command line – or may be parts of a single large program, called an integrated development environment (IDE). In many cases, particularly for simpler use, simple ad hoc techniques are used instead of a tool, such as print debugging instead of using a debugger, manual timing instead of a profiler, or tracking bugs in a text file or spreadsheet instead of a bug tracking system.

A GPL linking exception modifies the GNU General Public License (GPL) in a way that enables software projects which provide library code to be "linked to" the programs that use them, without applying the full terms of the GPL to the using program. Linking is the technical process of connecting code in a library to the using code, to produce a single executable file. It is performed either at compile time or run-time in order to produce functional machine-readable code. The Free Software Foundation states that, without applying the linking exception, a program linked to GPL library code may only be distributed under a GPL-compatible license. This has not been explicitly tested in court, but linking violations have resulted in settlement. The license of the GNU Classpath project explicitly includes a statement to that effect.

patch (Unix) Unix utility to apply changes to text files

The computer tool patch is a Unix program that updates text files according to instructions contained in a separate file, called a patch file. The patch file is a text file that consists of a list of differences and is produced by running the related diff program with the original and updated file as arguments. Updating files with patch is often referred to as applying the patch or simply patching the files.

<span class="mw-page-title-main">Richard Stallman</span> American free software activist and GNU Project founder (born 1953)

Richard Matthew Stallman, also known by his initials, rms, is an American free software movement activist and programmer. He campaigns for software to be distributed in such a manner that its users have the freedom to use, study, distribute, and modify that software. Software that ensures these freedoms is termed free software. Stallman launched the GNU Project, founded the Free Software Foundation (FSF) in October 1985, developed the GNU Compiler Collection and GNU Emacs, and wrote the GNU General Public License.

<span class="mw-page-title-main">History of free and open-source software</span> Aspect of history

In the 1950s and 1960s, computer operating software and compilers were delivered as a part of hardware purchases without separate fees. At the time, source code, the human-readable form of software, was generally distributed with the software providing the ability to fix bugs or add new functions. Universities were early adopters of computing technology. Many of the modifications developed by universities were openly shared, in keeping with the academic principles of sharing knowledge, and organizations sprung up to facilitate sharing. As large-scale operating systems matured, fewer organizations allowed modifications to the operating software, and eventually such operating systems were closed to modification. However, utilities and other added-function applications are still shared and new organizations have been formed to promote the sharing of software.

<span class="mw-page-title-main">GNU Emacs</span> GNU version of the Emacs text editor

GNU Emacs is a free software text editor. It was created by GNU Project founder Richard Stallman, based on the Emacs editor developed for Unix operating systems. GNU Emacs has been a central component of the GNU project and a flagship project of the free software movement. Its name has occasionally been shortened to GNUMACS. The tag line for GNU Emacs is "the extensible self-documenting text editor".

<span class="mw-page-title-main">Copyleft</span> Practice of mandating free use in all derivatives of a work

Copyleft is the legal technique of granting certain freedoms over copies of copyrighted works with the requirement that the same rights be preserved in derivative works. In this sense, freedoms refers to the use of the work for any purpose, and the ability to modify, copy, share, and redistribute the work, with or without a fee. Licenses which implement copyleft can be used to maintain copyright conditions for works ranging from computer software, to documents, art, scientific discoveries and even certain patents.

Proprietary software is software that is deemed within the free and open-source software community to be non-free because its creator, publisher, or other rightsholder or rightsholder partner exercises a legal monopoly by modern copyright and intellectual property law to exclude the recipient from freely sharing the software or modifying it, and—in some cases, as is the case with some patent-encumbered and EULA-bound software—from making use of the software on their own, thereby restricting their freedoms. It is often contrasted with open-source or free software. For this reason, it is also known as non-free software or closed-source software.

<span class="mw-page-title-main">GNU General Public License</span> Series of free software licenses

The GNU General Public License is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general use and was originally written by the founder of the Free Software Foundation (FSF), Richard Stallman, for the GNU Project. The license grants the recipients of a computer program the rights of the Free Software Definition. These GPL series are all copyleft licenses, which means that any derivative work must be distributed under the same or equivalent license terms. It is more restrictive than the Lesser General Public License and even further distinct from the more widely used permissive software licenses BSD, MIT, and Apache.

The following outline is provided as an overview of and topical guide to the Perl programming language:

References

  1. ↑ "Programming in C: A Tutorial" (PDF). Archived from the original (PDF) on 23 February 2015.
  2. ↑ Richard Stallman - 1989 - Announced through the GNU Bulletin and published with GNU software - https://www.gnu.org/licenses/gpl-3.0.html
  3. ↑ The Linux Information Project. "Source Code Definition" Archived 3 October 2017 at the Wayback Machine
  4. ↑ "gnu.org". www.gnu.org. Archived from the original on 3 July 2017. Retrieved 12 December 2015.
  5. ↑ Stallman, Richard (15 November 2017). "The JavaScript Trap - GNU Project - Free Software Foundation". Gnu.org. Retrieved 20 July 2022.
  6. ↑ Why Source Code Analysis and Manipulation Will Always Be Important by Mark Harman, 10th IEEE International Working Conference on Source Code Analysis and Manipulation (SCAM 2010). Timișoara, Romania, 12–13 September 2010.
  7. ↑ SCAM Working Conference Archived 29 September 2017 at the Wayback Machine , 2001–2010.
  8. ↑ Martin Goetz (8 February 1988). "Object-code only: Is IBM playing fair?". Computerworld . Vol. 22, no. 6. p. 59. It was in 1983 that IBM reversed its 20-year-old policy of distributing source code with its software product licenses.
  9. ↑ "Extending and Embedding the Python Interpreter". docs.python.org. Archived from the original on 3 October 2012. Retrieved 17 August 2014.
  10. ↑ "Interpreter Method - Techopedia". Techopedia.com. Retrieved 4 August 2022.
  11. 1 2 3 Spinellis, D: Code Reading: The Open Source Perspective. Addison-Wesley Professional, 2003. ISBN   0-201-79940-5
  12. ↑ "Art and Computer Programming" ONLamp.com Archived 20 February 2018 at the Wayback Machine , (2005)
  13. ↑ "Software Portability - CodeProject". www.codeproject.com. Retrieved 4 August 2022.
  14. ↑ P., Liu, Joseph; L., Dogan, Stacey (2005). "Copyright Law and Subject Matter Specificity: The Case of Computer Software". New York University Annual Survey of American Law. 61 (2).
  15. ↑ Apple Computer, Inc. v. Franklin Computer Corporation Puts the Byte Back into Copyright Protection for Computer Programs Archived 7 May 2017 at the Wayback Machine in Golden Gate University Law Review Volume 14, Issue 2, Article 3 by Jan L. Nussbaum (January 1984)
  16. 1 2 Lemley, Menell, Merges and Samuelson. Software and Internet Law, p. 34.
  17. ↑ "Info" (PDF). cr.yp.to. Archived (PDF) from the original on 7 June 2011. Retrieved 27 December 2019.
  18. ↑ Bernstein v. US Department of Justice Archived 4 April 2018 at the Wayback Machine on eff.org
  19. ↑ EFF at 25: Remembering the Case that established Code as Speech Archived 5 January 2018 at the Wayback Machine on EFF.org by Alison Dame-Boyle (16 April 2015)
  20. ↑ "License". www.apache.org. Archived from the original on 23 September 2015. Retrieved 27 December 2019.
  21. ↑ Hancock, Terry (29 August 2008). "What if copyright didn't apply to binary executables?". Free Software Magazine. Archived from the original on 25 January 2016. Retrieved 25 January 2016.

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