Exploring Functions Executed Before and After main() in C.

Introduction to Main Function in C

In C programming, the main function is the entry point of a program. There can be only one main function in a program. The operating system calls the main function to execute a program.

Contrary to popular opinion that functions are executed inside the main function, C provides a syntax that enables you to run a function before and after the main function.
This brings us to the concept of Constructors and Destructors.

Constructors

In many languages, constructors and destructors are Object Oriented Programming (OOP) concepts. C is not an OOP language.
Constructors are used to execute a function before the main function in C. You can try this out;

#include <stdio.h>

// Declaration of the constructor function
void before_main() __attribute__((constructor));

// Definition of the constructor function
void before_main() {
    printf("Before main function\n");
}

int main() {
    printf("Inside main function\n");
    return 0;
}

Before main function
Inside main function

Use Cases of constructors in C?

• To initialize global variables.

• Establish network connections.

• Initialize hardware resources.

• Used for memory allocation through dynamic memory allocation
  And so much more...

Destructors

It is commonly known that a C program ends with the return statement in the main function. However, you can execute functions after the main function with the help of destructors.

#include <stdio.h>

// Declaration of the destructor function
void after_main() __attribute__((destructor));

// Definition of the destructor function
void after_main() {
    printf("After main function\n");
}

int main() {
    printf("Inside main function\n");
    return 0;
}

Inside main function
After main function

Use Cases of Destructors in C?

• To clean up tasks such as closing network connections.

• Used in releasing hardware resources.

• Used for memory deallocation through dynamic memory allocation.

Conclusion

Even though C is not an object-oriented language, constructors and destructors still have their use cases in C.
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