To begin with, as an experienced developer having in-depth knowledge in C programming, I’ve been asked quite often about whether it is possible to write a program in C without using the main function. The answer is, yes, it is possible and I’m going to explain how this works. Certain compilers like GCC, allow this, and it’s a fascinating delve into the flexibility and possibilities of C programming. However, this move is considered non-standard. So why does this curiosity arise? It’s because traditionally, it’s said that the execution of a C program begins from the main function. This is true and works perfectly for most standard cases.
The _start() Function
The real beginning point in most C programs is actually a function called _start(). Usually, this is a bootstrap function that initializes the necessary resources and finally calls the main(). The _start() function is incorporated into your C program by the compiler, separately from your source code. Therefore, it already exists and is secretly doing its job behind the scenes without most developers needing to know about it.
Using the _start() in place of main()
The conceptual secret of running a C program without main() lies with bringing this _start() function into the arena and effectively using it in place of main(). This is exactly the trick that GCC compilers allow us to do. Here’s how:
void _start() {
// Add your code here
_exit(0);
}
Notice the use of _exit() function at the end. This is crucial because if the program doesn’t call _exit(), the program will crash.
Understanding the Program Flow
This is how the program will work: In standard C programs, the _start() function, provided by the compiler, would call the main() function. However, in this case, we have replaced the main() function with our own _start() function, and it directly executes instead of calling main(). The _exit() function is a system call that will terminate our program correctly.
A Note on Library Dependencies
- While it’s interesting to code a C program without main(), there are a few setbacks. This practice introduces a fair amount of library dependencies into your code. For instance, to use the _exit() function, the unistd.h library is necessary.
- This might not be a problem initially, but if you expect your code to run on different systems and environments, it’s recommended to stick with the main() function because it brings a higher level of portability.
In conclusion, we have seen how it is possible to craft a unique C program that runs without the main() function. This is a testament to the flexibility of the C language. It’s, however, important to note that this is a non-standard practice, so use with discretion.
