Editing Entry point (section)

===Contemporary===
In most of today's popular programming languages and operating systems, a [[computer program]] usually only has a single ''entry point''.

In [[C (programming language)|C]], [[C++]], [[D (programming language)|D]], [[Zig (programming language)|Zig]], [[Rust (programming language)|Rust]] and [[Kotlin (programming language)|Kotlin]] programs this is a [[Function (computer science)|function]] named <code>main</code>; in [[Java (programming language)|Java]] it is a [[static method]] named <code>main</code> (although the class must be specified at the invocation time), and in [[C Sharp (programming language)|C#]] it is a static method named <code>Main</code>.<ref>{{cite web |url=https://www.ibm.com/support/knowledgecenter/SSLTBW_2.3.0/com.ibm.zos.v2r3.cbclx01/mainf.htm |title=The main() function |publisher=[[IBM]] |work=ibm.com |access-date=2014-05-08 |archive-date=2017-09-10 |archive-url=https://web.archive.org/web/20170910083002/https://www.ibm.com/support/knowledgecenter/SSLTBW_2.3.0/com.ibm.zos.v2r3.cbclx01/mainf.htm |url-status=live }}</ref><ref>{{cite web |url=http://msdn.microsoft.com/en-us/library/acy3edy3.aspx |title=Main() and Command-Line Arguments (C# Programming Guide) |publisher=Msdn.microsoft.com |access-date=2014-05-08 |archive-date=2014-06-09 |archive-url=https://web.archive.org/web/20140609000508/http://msdn.microsoft.com/en-us/library/acy3edy3.aspx |url-status=live }}</ref>

In many major operating systems, the standard executable format has a single entry point. In the [[Executable and Linkable Format]] (ELF), used in [[Unix]] and [[Unix-like]] systems such as [[Linux]], the entry point is specified in the <code>e_entry</code> field of the ELF header. In the [[GNU Compiler Collection]] (gcc), the entry point used by the linker is the <code>_start</code> symbol. Similarly, in the [[Portable Executable]] format, used in [[Microsoft Windows]], the entry point is specified by the <code>AddressOfEntryPoint</code> field, which is inherited from [[COFF]]. In [[COM file]]s, the entry point is at the fixed [[offset (computer science)|offset]] of 0100h.

One exception to the single-entry-point paradigm is [[Android (operating system)|Android]].  Android applications do not have a single entry point{{snd}} there is no special <code>main</code> function. Instead, they have ''essential components'' (activities and services) which the system can load and run as needed.<ref>{{cite web |url=http://www.linuxtopia.org/online_books/android/devguide/guide/topics/fundamentals.html |title=Application Fundamentals |work=Android Development |access-date=2014-02-19 |publisher=linuxtopia.org |archive-date=2013-12-31 |archive-url=https://web.archive.org/web/20131231125154/http://www.linuxtopia.org/online_books/android/devguide/guide/topics/fundamentals.html |url-status=live }}</ref>

An occasionally used technique is the [[fat binary]], which consists of several executables for different targets packaged in a single file. Most commonly, this is implemented by a single overall entry point, which is compatible with all targets and branches to the target-specific entry point. Alternative techniques include storing separate executables in separate [[fork (file system)|forks]], each with its own entry point, which is then selected by the operating system.