In computers, an entry point is the point in a program, module, or function where the code begins; specifically, the memory address where it starts. In a program, it is the first code module, or even the first line of code, that is executed. In a linear program like BASIC or COBOL, the entry point is literally the first line of code. The code continues sequentially until some type of jump or call is executed. In modular programming, like all variants of the C programming language, the entry point is the starting module. In C, it is the “Main()” function.
In modular programming, such as the C++ programming language, the entry point is the starting module.
In older programs and operating systems, a program may have multiple entry points, depending on the function or system it is running. On most modern operating systems, including Windows® and Unix, programs are written in languages that support a single entry point. Even in the early days of modern computing, languages like BASIC, while having a single entry point for the program, can support “long jumps”, in which the program can “jump” from one module to the entry point from another module indiscriminately. . This was encouraged by what we call “spaghetti code”, which was difficult to maintain or modify.
An entry point may not even refer to the entry point of a program, but it could be the entry point of a dynamic link library (DLL), which are sorts of mini-programs shared by other programs. A DLL file that handles keyboard input is an example. Regardless of the type of program, module, or function, the entry point is the single point where processing begins on that piece of code. The key to understanding any language or modifying and supporting any program is to understand how the entry point is identified in that particular program or operating system.
The concept of entry points was implemented when computer programming left the completely linear methods of the early days. Back then, a computer program started at the first line of code and continued one line at a time until the end of the process. Soon, programming constructs like loops, conditional branches, recursion, and others created programs that were functionally more efficient, but processing jumped everywhere within the code. The nature of these programs means that there can be many lines or sections of code before the point where processing actually begins. For this reason, the entry point was created and identified.
In C, this became the main() function. Regardless of where this function existed in the code, that’s where the processing started. In other languages, entry points are identified not so much by where they are, but where they are not. The beginning of the program can contain sections of variable declarations and subroutines. The first line of code after these areas or functions, by default, becomes the entry point.
