Entry point

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In computer programming, an entry point is where control enters a program or piece of code.

Usage[edit]

Contemporary[edit]

In most of today's popular computer systems, such as Microsoft Windows and Unix, a computer program usually only has a single entry point. In C, C++, D and Kotlin programs this is a function named main; in Java it is a static method named main, and in C# it is a static method named Main.

One notable modern exception to the single-entry-point paradigm is Android. Unlike applications on most other operating systems, Android applications do not have a single entry point – there is no main() function, for example. Instead of a single entry point, they have essential components (which include activities and services) which the system can instantiate and run as needed.[1]

Historical[edit]

Historically, and in some contemporary legacy systems, such as VMS and OS/400, computer programs have a multitude of entry points, each corresponding to the different functionalities of the program. The usual way to denote entry points, as used system-wide in VMS and in PL/I and MACRO programs, is to append them at the end of the name of the executable image, delimited by a dollar sign ($), e.g. directory.exe$make. The Apple 1 computer also used this to some degree. For example an alternative entry point in Apple 1 BASIC would keep the BASIC program[clarification needed] useful when the reset button was accidentally pushed.

References[edit]

  1. ^ "Application Fundamentals". Android Development. linuxtopia.org. Retrieved 2014-02-19.